Is it normal to wake up at like 2 am, shaking like crazy????

Okay....this doesn't happen everyday..but whenever i have to go to the airport, or wake up reeeeeeeaaaallllly early, I always wake up shaking frantically. I don't know why, but it's really scary. No matter if im cuddling in my snuggie, wearing warm clothes, or curled up in bed, im shaking for over an hour. Whenever i go on snowboarding trips, im shaking for like half an hour. if im at the airport, i dont stop 'till im done security, and if im at basketball practice, well its not bad, i just randomly shake for like 10 minutes. Someone pleeeeeeeaaaazzzzzz tell me what this mite be...i'll be travelling soon, and if i wake up shaking again, i really need to know what's going on.