Shaking While Trying to Fall Asleep

I have read in places about people shaking and moving around uncontrollably while sleeping (Such as periodic limb movement disorder), but as far as I know, I do not suffer from this.

For the last few years, I have had occasional nights where I cannot get to sleep because of a constant compulsion to shake myself about when I'm in bed. This isn't just a case of uneasiness or irratation, it is involuntary. I simply cannot stop this erratic, sometimes convulsive behaviour.

It goes away after a while if I stand up, turn the light on or go around the house as if it was daytime. It only started happenning after one particular night when I was about 14 (I'm 18 now), when I was sleeping, lying on my back and I got the feeling that I couldn't breathe. I could hear my pulse going quite slowly but loudly, and then I woke up sweating and unable to get back to sleep.

Anyway, it also used to happen now and then during the day, if I was in an assembly or any kind of event which relied on me staying still, which leads me to believe that it can be brought about by general anxiety.

During these times, my chest feels faint. At the back of my mind I get the idea that if I stop moving, my heart will stop. I know that sounds stupid and entirely unreasonable but that's kind of a subconscious feeling.

I'm sorry for the long post, but if anyone suffers from the same thing or has any idea how to reduce the effect then I would appreciate a reply. It only seems to happen when I worry about it happening. If I could forget about it, then it might go away.

I've never really talked to anyone about this, but people have been noticing it when I begin shaking and twitching in public. I'll go back to bed now, its 5:27 am.