why did i suddenly become so socially anxioua

i am 18 and the past 2 years have been the worst as my social anxiety has just exploded to the point where i will have panic attacks and breakdowns if i have to go somewhere i know there are alot of people or where i cant get out of. before this i was very social and went to school fine and was doing well but this anxiety has caused me to leave school and now i dont have any qualifications and it feels like my dream of being a psychiatrist is over but i just dont understand how i can go from going to school and going out with friends fine and then it turns into panic attacks and breakdowns it doesnt make sense and i cant seem to thjnk of a reason why this happened.