I have 'cold chills' several times a day, even when I'm not cold. What are these?

For the past few months, I'll be carrying on my normal activities and just randomly shake all over. Sometimes, I'll get a very 'anxious' feeling, like the feeling you get when something bad happens, and I shake a couple of times in a minute. What could this be? At first I thought it was just stress from school, but I've been home from break for a while and they're still occurring. Thanks reddit!