Why did a very bad experience with a recreational drug cause my anxiety disorder? i'm not a drug abuser, i tried it once. ( bad decision )

Not likely: It is not likely that using a drug once could cause your anxiety to last for an extended period of time. Lots of things can give people anxiety, especially if you are a high achiever. I think you can make an appointment with a psychologist to evaluate the problem and make suggestions would be good. Not all anxiety is bad, it just has to be managed and channeled.

Now It's a Memory: Sadly, trying one of today's "designer" drugs even once can create memories of a terrifying experience. Though promoted as "pure, " you can never be sure of what or how much you're taking. Now you are likely reacting to the memory of what happened, rather than the drug itself. So treatment similar to that used with ptsd should help. A therapist who treats anxiety can help you understand and heal.