I've started a bad habit of falling asleep with my left foot hanging off the bed and when i wake up, it is swollen. my ankle also swells up. i'm scared that i'm going to get clots. can i?

What is the question: If you are producing blockage of return of blood from your veins and it is creating peripheral swelling then you have to solve the problem producing this. Am not sure that altering your sleeping positions is a medical issue, but rather something to be discussed with a sleep engineer if there is such a thing.

Don't worry: Unless you have a history of dvt, are a smoker or have other risk factors, the risk of clots is small. Just in case...Try sleeping toward the center of the bed.

Blood clots: Simple thing would be to put something like a pillow or bed rail to prevent leg from falling off bed. Doubt you would get a clot but gravity will cause blood pooling and then swelling.