I feel lightheaded/dizzy very often,with hot flashes at times. i'm 21,and do have anxiety a lot but haven't been anxious for weeks.anxiety the cause?

Possibly: It's definitely possible that anxiety is the culprit, however that is not the only possibility. It would be a good idea to have an exam and get some labs done to make sure everything is alright with your physical health as well. Anemia, electrolyte problems, infection, medications, drugs/alcohol/tobacco can cause it as well, just to name a few.