After falling asleep, 60-90 minutes later slowly awaken to feeling cold, although room is warm, experience intense wavelike, torso internal vibrations/tremors/spasms, intensity and duration vary thru awakened state. cause? prevention? treatment?

Currently, these are spells of unclear etiology. You will have to undergo some testing, including a sleep study to arrive at a more definitive answer. Panic attacks can present this way, however you should have medical evaluation and guidance to rule out certain underlying causes including thyroid problems, movement disorders in sleep, and seizures to name a few. Talk to your doc and good luck!