Sounds like health anxiety to me.
One thing that helped me when I used to get panic attacks was reading that they are perfectly normal, healthy reaction to fear. The adrenaline rush and all the physical symptoms it causes (tight chest, heart palpatations, tight throat, dizziness, spaced out feeling) are all signs your boday is actually working the way it should. The problem is soley in the mind when it comes to anxiety.
Its a vicious circle, you become afraid of having a panic attack, which in turn brings them on. My gran said to me: when you get a panic attack, try to make it worse, you will find they never get as bad as you think...ie, no matter how bad, you dont die! Reducing my fear of having them and understanding them better helped me feel a lot more calm about them which reduced the amount I actually got.
I was given various medicines to help with my panic attacks. They started after the death of my brother, I think with him being the first dead person I had ever seen and being so young, it set off a fear of death in me which meant the slightest health problem and I was convinced it was serious. I had cipralex, a form of citalopram which made everything much worse. Then they tried propanalol (beta blocker) which made my heart beat too slow. Medication didnt help with me, finding out what my trigger was for the panic attacks and dealing with it, coupled with as I have had already said, understanding more about panic attacks, and time was what helped in the end.
A good breathing exercise I found helped me. Alternative breathing. Close one nostril with your thumb, leave the other open. Exhale through your nose, then swap nostrils, close the other side, open the other and inhale. Keep doing that and it wont be long till you are feeling sleepy.
Another one I learned was to tense up my muscles and release. Lying on your back, starting from the feet, tense up and stretch out your muscles for ten seconds or so, then totally relax. Ankles, calves, knees, thighs, bottom, hands, arms, back, shoulders and neck. As tight as you can, then relax. It helps relieve the tension from feeling panicky.
I would also suggest that when you are lying in bed and feel like you cant sleep and are getting anxious, get up. Dont lie there and keep trying. Get up and distract yourself for fifteen minutes or so. Sip on a glass of water, read a short story in a magazine...then try again. I found the more I tried to sleep and couldnt, the more stressed I got. I still have this now, but its insomnia not anxiety anymore.
Cammomile tea helps too, its a very mild natural sedative, so a cup half an hour or so before bed can wind you down a bit.
I do agree with the other posters though, I would go back to the GP and explain whats going on so they can make sure there is no medical cause for your panic attacks/anxiety and if it is psychological, they can refer you for some help with dealing with it. You have my sympathy, I wouldnt wish panic attacks on my worst enemy.