Ok here it is, the (hopefully) final version. I've added a section on coping strategies and complications of HG and shifted a few bits and pieces around. I couldn't find that entry from jonnyd1 about the Rules. Hopefully I've covered most of them anyway. Thanks to everyone who contributed. Let me know what you think. ignore the formatting it disappears when i paste it in, but it'll be there in the real version.
Hyperemesis gravidarum (HG) is a severe form of pregnancy sickness which affects between 1 and 3% of pregnant women. Historically, it was mistakenly thought to be a psychosomatic illness and women were treated as though they had a psychotic disorder. This view has been comprehensively disproven by numerous research papers in recent decades, and it is now known to be an illness of organic origin, although its causes have yet to be fully understood. There is a persistent common belief that no drugs should be given to women in the first trimester of pregnancy. This is not true. There are a number of effective anti-emetic (anti sickness) drugs which can safely be taken in early pregnancy. Unfortunately, the erroneous views that HG is a psychosomatic conditions and that no drugs are safe in the first trimester still persists in many places, shockingly, even amongst GPs and midwives. Sadly, many women still come across unsympathetic health professionals who are ignorant of current treatment methods. The following guide has been written by women who have suffered from HG and have direct, first hand experience of it.
Facts and Figures and FAQs
HG is worse in the first trimester for the majority of sufferers, though a significant proportion (10 ? 20%) suffer for the entire duration of the pregnancy. If you have close relatives (mothers, sisters) who have had HG, you are also at significantly higher risk of being a sufferer yourself. HG is the most common cause of hospitalisation of pregnant women in the first trimester.
How do I know if I have HG?
If you are suffering from persistent nausea and/or vomiting which is preventing you from eating and/or drinking then you may be suffering from HG. With ordinary nausea and vomiting of pregnancy (NVP), the sickness does not interfere with your ability to eat and drink enough, you should not be losing weight and you should be able to continue to care for yourself and your family although you may not be feeling too great. With HG, sufferers often need help caring for themselves, never mind look after their family. The illness can be completely debilitating for weeks or even months. If you're not sure, the Hyperemesis Education and Research (HER) website have a fact sheet to help you determine whether or not you are suffering from HG or NVP.
www.helpher.org/mothers/hyperemesis-or-morning-sickness/index.php
Diagnosis is important as you will inevitably become dehydrated and you will need to be admitted to hospital for IV rehydration. Starvation is another risk. When your body burns fat for energy, it produces chemicals called ketones which can be detected in your urine. You can monitor your levels of starvation using ketosticks, available from pharmacies. You pee on the stick and it monitors your levels of ketones. If levels are high, you should tell your doctor or midwife. If you are worried about dehydration and ketone levels and you can't see your doctor or midwife, you can go to A&E.
What are the treatments?
Initially you will be advised to use non-pharmacoligical strategies which are similar to the general advice given to any pregnant women suffering from nausea. These include eating little and often, eating protein-rich, low-fat meals, avoiding triggers of nausea such as strong smells and getting enough rest. You can try ginger, seabands (accupressure wristbands used for travel sickness) and extra doses of vitamin B6. Avoid getting out of bed in the morning without something in your stomach such as a tea biscuit, toast or cracker. Some women find that these measures give relief in the initial stages of HG but they become ineffective once the illness is in full swing.
The next line of treatment is prescribed antiemetics such as phenergan, cyclizine, stemetil and ondansetron. For many women these work well and control the nausea and vomiting enough for them to eat and drink normally and regain some of their lost weight. Many can even return to normal life. You may find that one antiemetic on its own is not effective and you may need to try different combinations but you can discuss this with your doctor. Even with antiemetics, you will probably still need to use coping strategies such as getting extra rest, eating small frequent meals and avoiding triggers when the HG is at its peak. If you are dehydrated, you may be admitted to hospital for IV fluids. Minerals and vitamins can be added to the drip to replace any you may have lost, as well as antiemetics.
Unfortunately, antiemetics don't work for everyone. If they are ineffective, you should be referred to an obstetrician (if you haven't been already) for the next line of treatment, which will probably be steroids. These carry a small risk of cleft palate, but this will be discussed with your doctor. In a small number of cases even this is not effective and drastic treatments such as feeding with a tube directly into the stomach may have to be considered.
The Royal College of Obstetricians and Gynaecologists in the UK have no guidelines on the treatment and management of HG. However, the American College of Obs/Gynae (ACOG) and the Society of Obs/Gynae of Canada (SOGC) have published guidelines which can be found at the following sites

www.sogc.org/guidelines/public/120E-CPG-October2002.pdf 

www.guideline.gov/content.aspx?id=10939
These documents give detailed information about treatment protocols for HG.
My GP is unsympathetic and refuses to prescribe me drugs - what should I do?
Unfortunately this experience is all too common. In this case you should see another GP if possible. You should also ask for a referral to an obstetrician. If you remain untreated and become dehydrated, you can have yourself admitted to A&E for IV fluids and ask to be seen by an obstetrician.
Do alternative remedies work?

Some women are greatly helped by alternative medicine, particularly Homepathy and Acupunture. Some women can claim to have had the illness 'stopped in its tracks' by Acupunture, but success varies between individual patients and it tends to be expensive. These remedies are worth a try if you can afford it but have a back up plan incase it doesn't work.
Is it worse carrying a boy or a girl?
There is conflicting evidence as to whether having a boy or a girl makes HG worse, some studies say boys, some say girls.
Is it worse with twins?
Yes there is evidence that carrying more than one baby makes HG worse.
Will my baby be ok?
Babies born to HG mothers are usually absolutely fine. If you lose some weight during the first trimester the risks for the baby are low as it does not need much nutrition at this time and your body should have enough stores from before your pregnancy. However, if you continue to to lose weight due to lack of treatment or failed treatment, then there is an increased risk of low birth weight or pre-term birth. Studies show that this is a risk for women who are severely ill, are dehydrated for long periods and lose more than 10% of their body weight.
There is also growing evidence of long term health effects in some children born to mothers who suffer malnutrition in pregnancy. In some cases this is not evident until adulthood with increased risk of chronic conditions such as diabetes and hypertension.
Please note that the risk of any harm to the baby is still small, but it is increased compared with women who have not been dehydrated or starved. If you have HG and you were successfully treated so that you did not lose too much weight and were not dehydrated for a long time, then there is no increased risk.
For more information see the following links
forums.helpher.org/viewtopic.php?t=18
www.helpher.org/hyperemesis-gravidarum/complications/fetal-programming.php
I've heard that being sick is a sign of a healthy pregnancy, is this the case with HG?
You will often be told that morning sickness is a good sign and feeling sick means the pregnancy is well established. This is generally the case with normal NVP, however, it is not the case with untreated HG. There is actually a higher risk of pre-term birth and low birth weight. However, continuing to feel sick may be a sign that the pregnancy is still progressing. Some women with HG who miscarried reported that the first sign was that they suddenly stopped feeling sick.
How long will this last for?
For most women, HG peaks in the first trimester and tails off or disappears completely later in the pregnancy. The usual advice for morning sickness is that it will improve after 12 weeks. The majority of HG sufferers find that it takes longer than this. Unfortunately, some women suffer severely for the entire pregnancy. Others find that it improves, but they suffer from nausea and occasional vomiting until birth. Relapse is quite common especially if you have tried to return to your normal busy life. There is a great temptation to make up for lost time and become very active once you start to feel better, but this very often leads to the nausea returning. You should be very careful about resuming work and normal household activities even if you feel as though you're up to it. Be careful too about stopping your medication, do it very gradually and resume at the first sign of the condition returning. You may have to continue to take it for the entire pregnancy to prevent a relapse.
All I can drink is coke, I'm worried that I'm not eating a healthy diet.

Through pregnancy, we are bombarded with advice about what to eat and what not to eat. Women with HG often find that the list of food and drinks that they can keep down is very small and not at all from the healthy options. Many women find that eating vegetables and some fruits causes immediate vomiting in the peak stages, making it even more difficult to follow a healthy diet. For some reason, women with hyperemesis ofen find sweet and salty foods ie, sweet drinks like coke, and crisps, are more likely to stay down than healthy foods. Their peculiar diet can lead to disapproving comments and the incorrect assumption that this is how they normally eat. 
Various women find different drinks acceptable. Coke (often left to go flat) Lucozade, lemonade, milkshakes and IronBru, Dr Pepper, orange squash, apple juice, lime juice, ice cubes made of flat coke or just tapwater, ice lollies and sips of tepid water can help in keeping rehydrated. 

When the illness is at its worst during the early hormonal surges - typically between eight and ten weeks- then it is difficult to retain any liquids and you may need to be hospitalised for rehydration at about this time. 

When solids do become bearable,jelly, tinned fruit, ice lollies, ice cream, crisps, fish fingers, potato cakes, crumpets, soda bread and similar potato based or salty foods have often been found to be acceptable. If you can eat food with a high water content such as melon, cucumber, apples and other fruits, it is a good way of taking some fluids on board without having to drink water. If you develop a craving for something then go with it, it may be your body's way of getting a nutrient it needs.
The important thing to remember at this time is that it doesn't matter what you eat or drink, the crucial thing is that you eat or drink something. Don't forego something because you are worried that it's bad for you. In a normal diet, too much salt and sugar is bad for you, but when you consume nothing else, this may be your only source of calories, fluid and salt for the day. Instead of berating yourself for your unhealthy diet, congratulate yourself that you have kept something down because your body needs it. If you are able to take vitamin tablets or syrups, then do so but most women find that large multivitamin tablets make the nausea worse. You may be able to get vitamins that dissolve under your tongue which you may be able to tolerate. If and when you begin to feel better, you can start to re-introduce more healthy food.
Coping Strategies
The most important coping strategy is to get as much rest as you can. HG is an episodic condition with frequent periods of recovery and relapse. Many HG sufferers report that trying to do to much during periods of partial recover very rapidly results in a relapse.
Avoid thinking ahead more than the next few days. Torturing yourself with 'I have 20 weeks of this left to go' is not helpful. If you have small children to look after do everything in your power to sort out childcare - rely on relatives, nurseries and friends. Don't feel guilty about needing help, you are very ill and you would not be expected to carry on regardless if you were undergoing treatment that causes similar symptoms such as chemotherapy. The house may be a tip, there may be a washing mountain and the kids/your partner/work may have to fend for themselves for a while but if you push yourself your vomiting will get worse. If you have HG you need to give yourself a break and know that normal service is not applicable.
Avoid becoming dehydrated. If you can't tolerate drinks, try sucking ice cubes made of juices, or sipping very slowly through a straw. If this doesn't work, then be prepared for a hospital admission, don't try to fight it - if the GP says you need to be admitted you must go. A drip and having antiemetics injected can give you days/hours of respite that are so important not only to your physical welfare but your mental well being too.
At all costs avoid triggers of nausea. Strong aversions to various foodstuffs and food smells are common in most if not all women suffering HG. For some the slightest thing will trigger nausea, including even the sight of food or hearing someone talking it. Many women find that once they have thrown up a certain food, they cannot bear the sight of it again until the HG improves. For some women an aversion can have such a strong association that they still cannot eat certain things even after the pregnancy. Cooking smells are often unbearable so avoid cooking as much as possible and make sure that windows are open and you are far from the kitchen while it is going on.
Lying alone in bed or on the sofa can be boring and depressing. Get yourself some DVDs of your favourite TV shows or films, preferably comedy to try to lift your mood. If watching TV makes you nauseous, try radio or get some talking books. If you have friends who can come over for a while and just be around it will help a lot with the lonlieness and isolation that many sufferers feel.
Complications of HG
The effect of dehydration, vomiting and malnutrition can have knock on effects and lead to a number of associated symptoms.
A very common side effect of dehydration is constipation which can be severe, painful and distressing. Rehydration is important to deal with this. Once you are able to drink again, you can take fybogel, it's unpleasant but effective. In difficult cases glycerin suppositories are helpful. Headaches, cracked lips and mouth sores are other common side effects of dehydration.
Repeated vomiting can cause tears in the gullet, called Mallory-Weiss tears which cause you to bring up fresh, red blood. If you bring up vomit that looks like coffee grounds you should seek immediate medical attention as this is old blood and can indicate a bleed further down.
Acid reflux, which can lead to hiatus hernia is also fairly common. You doctor can prescribe an antacid if you can tolerate it.
Low iron and vitamin levels can cause problems and should be checked if you have had an inadequate diet for a prolonged period.
Teeth may suffer from acid in vomit and bile. Moreover, many women find that they can't brush their teeth as it stimulates their gag reflex and makes them vomit. You may have to use a mouth wash and speak to your dentist. Make your dentist aware of the problem so that they can advise you and also so that they go easy during examinations so as not to trigger a vomit.
Sleep disorders are common in HG. It seems particularly cruel that the only time you have relief from nausea is during sleep, and even though you are exhausted from starvation you still cannot get to sleep. Some women find that antiemetic medications that make you drowsy, such as phenergan, or cyclizine are helpful in this situation.
Ptyalism (hyper salivation) can be caused by repeated vomiting. This is quite unpleasant and some women find that that swallowing their own saliva makes them vomit. It may be necessary to carry around a cup to spit into.
Ante-natal depression, post natal depression (PND) and post traumatic stress disorder (PTND) are risks of HG. It is very difficult to keep your mood elevated when you are suffering the continual physical and emotional misery of HG. Treatment of the HG and relief of symptoms is probably the most effective way to avoid associated depression, but where this is not possible or treatment doesn't work, be aware that it is a very real risk and speak to your doctor about strategies to avoid it. Having had HG puts you at greater risk of PND, partly because of the greater difficulty you will have in coping with a newborn when your own reserves are so depleted. Be aware also that PTND is a possibility. HG is an extremely traumatic condition and some women have flashbacks and nightmares. 

Will it go away when I give birth?
The good news is that for the vast majority of sufferers the physical symptoms of HG disappear completely as soon as the baby is born. You should be aware though that it is not unknown for the nausea to persist after birth especially if you have been severely ill. If this occurs, speak to your doctor. For women who suffered persistent, long term nausea and vomiting, it may take some time to restore energy levels and nutritional reserves. Moreover, while the physical symptoms may leave, the trauma of HG can leave an emotional legacy for many women, especially when combined with the rigours of caring for a baby. If you have any concerns, speak to your doctor or midwife. Don't feel that you should just be able to pick yourself up and get on with things, if you're having problems you are entitled to seek support.
Will I get it in my next pregnancy and will it be the same?
Unfortunately, having HG in one pregnancy puts you at a high risk of suffering in subsequent pregnancies although it is possible to escape it. Some women find that the HG gets better in subsequent pregnancies, whereas others find it stays the same or gets worse. There is really no way of knowing how your pregnancies will relate to each other.
Can I do anything to prepare for HG incase I get it again in my next pregnancy?
The HER website has a page of advice on preparing for your next pregnancy. forums.helpher.org/viewtopic.php?t=17. If you had medication which worked for you in your previous pregnancy, make sure that you have it ready to take as soon as you feel ill. Studies show that the quicker you get on top of the sickness, the better the medication works. Because HG can start within days of missing your period, see your GP as soon as you know you're pregnant.
I have never known anyone with HG. Where can I talk to women who understand how I feel?
There is a support thread on the talk boards here (ask MNHQ to add link) which is run by sufferers and ex-sufferers. There are discussions of practical issues such as tips for coping and medication but the real value of this forum is that you get sympathy and understanding from people who know exactly what you're going through. If you just want to moan or let off steam, you are free to do so and nobody will hold it against you. Comments are also welcome from relatives, partners, friends and carers of HG sufferers. The HER website also has talk boards at forums.helpher.org/. There is also a UK based yahoo group called Bloomingawful at health.groups.yahoo.com/group/bloomingawful/
Dealing with well meaning but unhelpful advice
Women with HG are often told by friends and family that it's just morning sickness, a normal part of pregnancy and you just have to put up with it. Many HG sufferers report extreme frustration at being advised to try ginger, dry crackers or eat little and often. Most of them have tried every remedy they can think of to no avail. Because most women are familiar with NVP, there is often an attitude of, well I had morning sickness and I just got on with it. HG sufferers are often left with the feeling that they are whingers and malingerers and that if only they could adopt a positive attitude then they would be fine. This can lead to further depression in what is already a depressive condition. In order to deal with this, it is important that the HG sufferer has some supportive friends or family who can firmly but politely fend off these comments. The sufferer will often have no energy to deal with it herself. If possible explain to the person giving the advice that you are not suffering from morning sickness, you are suffering from a condition called hyperemesis gravidarum and direct them to sources of information.
Useful sources of information
Pregnancy Sickness Support is a UK based organisation run by GPs and midwives with direct experience of HG. They have a helpline which you can call for advice ? if nobody answers you leave a message and a midwife will call you back. They will be able to answer your questions about treatments and they keep a note of doctors around the country who are known to be sympathetic to HG sufferers and are willing to treat it with medication. Their website is at www.pregnancy sicknesssupport.org.uk
The Hyperemesis Education and Research Foundation (HER) is a US based foundation which was founded by HG survivors and has a mission to research the causes of HG and provide information and support for other sufferers. They have links to the latest scientific research and are actively involved in funding research, although you usually have to live in the USA to take part. There are loads of threads on every topic related to HG from women who have been through it, including very useful information about which treatment regimes worked. Their website is at www.hyperemesis.org.