Hi Floopy
You need to go to your GP and be checked out. It could well be anxiety attacks, but breathlessness, nausea and a sense of impending doom can also be indicators for heart problems, so you really need to be checked over.
I suffer from nighttime anxiety attacks, where I wake from my sleep covered in sweat, unable to breathe and in a complete panic. Oddly they tend to be worse when I have less to worry about, probably because I am so used to running on adrenaline that when things settle I can't come down and there's nowhere for all that adrenaline to go.
My GP gave me the choice of anti-depressants (some of which are specifically designed to control anxiety attacks) beta-blockers - which are very good at controlling the physical symptoms of an attack or something like valium (which he didn't recommend and I didn't want anyway). He also referred me to the healthy mind teams for some Cognitive Behavioural Therapy.
If you're feeling pent-up and in need of releasing all that excess nervous energy, the best thing I've found is exercise. Prior to breaking my ankle last year, I was walking 5 miles a day most weekdays and it made a huge difference, in fact the anxiety attacks only started once I was incapacitated and couldn't walk my stress off.
Its very difficult for advise the best way to handle the attacks when they happen, but for me reminding myself that its not serious or life threatening and will soon be over and concentrating on breathing deeply and slowly (long in and out breaths) are the main things that work.
Long-term, finding something that helps you to keep your stress levels steady, such as yoga or meditation can help minimise the chances of having an attack.
This article is quite good and has a fee tips.