So I thought I'd make a little landing pad for any MNers who suspect themselves or are curious about ADHD. We also have a lovely Neurodiversity support thread, which tends to run much better long term (ADHDers tending to not be fantastic at remembering to post on such a thread 
)
If you don't like reading long threads, there is a brilliant video here which (attempts to) explain in one minute what adult ADHD looks like, because it's so different from the stereotypes that we often have in mind about ADHD. vimeo.com/141104970. You can skip the rest of my OP 
For those who prefer reading I'll try to explain some of the main symptoms and/or signs and how it differs. As the guy in the video says, you don't need to have all of the signs to have ADHD, and nobody does.
There are thought to be three main areas where ADHD (ADD is an older name but they are the same thing) affects people: Impulsivity, Inattention and Hyperactivity.
Impulsivity (caused by ADHD) in adults often looks like this:
- Difficulty managing money
- Often interrupting or interjecting into conversations inappropriately
- Emotional disregulation - being quicker to anger, upset, or excite than other people generally.
- History of unsuitable relationships or trouble holding down a relationship
- Jumping around in conversation leaving others confused
- Lots of half finished projects or tasks - feeling like you're always starting things but never accomplish much.
- History of many different jobs, education directions or hobbies.
- A general dislike or disdain for the idea of routines and schedules
- And of course the obvious - being generally impulsive, easily distracted and starting lots of activities at the last minute. (But this is not the only or a necessary sign)
Inattention caused by ADHD in adults looks like:
- Time blindness - always being late for things and/or losing track of time.
- Disorganisation, messiness, general sense of chaos despite attempts to organise.
- Finding it difficult to stick to plans or goals and not really knowing why
- Reporting less success than other people using organisational aids such as calendars, to-do lists, reminders and diaries.
- Forgetfulness - sometimes forgetting entire conversations, forgetting an important task repeatedly or forgetting things which you do regularly.
- Contrary to (but coexistent with) the impulsive point, a tendency to do nothing and/or procrastinate when you don't have a set timetable or schedule.
- Chronic procrastination - to the point of missing or underperforming at things which are important to you
- Difficulty focusing, especially if a task is repetitive or long, but with a tendency to focus for long times at the expense of all else sometimes.
- Less care taken while driving leading to minor accidents or detours.
- Difficulty keeping in touch with friends or in the inner circle of friendship groups, especially as you age and lose regular connections such as school, university or work.
Hyperactivity in ADHD adults is the one which looks LEAST like expectations. It's things like:
- Talking a LOT and/or very fast
- Chatterbox brain - having 100 thoughts whirling around at once all the time
- Always needing to be "busy"
- Fidgeting and fiddling - finger tapping, foot tapping, swinging legs in a chair, chewing things, smoking, fiddling with hair, picking spots/scabs
- Difficulty falling asleep at night
- Addictive behaviour or history of - abuse of drugs or alcohol, smoking, caffeine addiction/dependency, risky sexual behaviour, internet/video game addiction, shopping or gambling addiction, exercise addiction, etc etc.
- Unexpected results from mild stimulants and depressants - usually swapped. Medicine with a side effect of drowsiness wakes you up and stimulants have little effect or make you feel productive and/or sleepy. (Sometimes causes the addictive behaviour as an attempt to self medicate)
And some general correlations:
- Having dyslexia or another related disorder (ADHD is often comorbid with other disorders, and dyslexia is the most likely to have been diagnosed in the UK if you were at school in the 80s-00s)
- Sensory seeking or avoidant behaviour - disliking textures of certain clothes or foods, finding loud noise or bright light difficult.
- Teenage pregnancy (and by association, being born to a mother who experienced this even if you weren't that baby from that pregnancy.)
- Having a close relative, including a child, who also displays signs or symptoms of ADHD.
- Having tried countless self help books but none have been in the slightest bit effective.
As a child:
- You might have been described as a "daydreamer" or were often being told off for chatting when you shouldn't have been.
- You tended to produce work - especially homework and coursework - which was much lower than the standard expected or the level you worked at in class, and teachers often expressed a sense that you "weren't trying hard enough".
Adults (especially women, and some girls) do NOT tend to:
- Get up and walk out of meetings when you are expected to be still
- Have a history of violent behaviour
- Run around acting without any inhibition at all
- Do something to the extreme or not at all
These are ADHD behaviours but more often seen in boys and men.
Well, this ended up really long Anyway, jump in! Don't be shy! :)