Can drugs cause trauma?

About 6 months ago my boyfriend and I tried this "legal drug" or so called legal in the UK called bzp or party pills. After taking the pill the first hour I was fine. I felt a little wired and out of it, like any other normal drug trip. One hour later I felt uneasy and slightly frightened. All I remember was hearing imaginary music play over and over in my head and seeing violent images. I felt like I was flying and monsters were chasing me. It felt very similar to a hallucinogen trip. I had never used or had experience with any hallucinogen drugs.

Now, 6 months later, I feel out of it and disconnected from this world. I have flashbacks of that day and they break me down to the point of tears. My question is has anybody else experienced this? How can I get rid of the trauma and frightened feeling I have to this day?

I've never tried BZP but it's possible for hallucinogen-like drugs to cause HPPD (flashbacks). I see some possible ways to solve this but they are mostly uneasy.
BZP sharpens senses and makes everything more intense. A small thing that makes you happy may cause you go ecstatic while a small sad thing may cause you go hysteric. Emotional memory leaves strongest and long lasting engrams(memory marks).

So how can you change it ?

First (safe) - you can use self-hypnosis or do a hypnosis session with a friend. In a relaxed state, safe atmosphere you remind yourself this event with all these traumatic feelings and you change it with a situation you imagine. You also should convince your subconscious to forget this as the situation is changed. You are safe now and the effects of the drug are over. Someone who leads this hypnosis should be cautious and gentle as in that time you confront your fear just like it would be happening to you now as it was then. You can also try holotropic breathing.

Second (risky) - provide best set and setting for yourself, people you trust and take a legal psychodelic substance again in order to reset the feelings towards it (the best is to use more safe analogue, like MDMA-ecstasy, it was used in psychotherapy in relieving bad memories until it was banned). The best would be to go with someone who is experienced in hallucinogens and the way to treat it. This method works for LSD or psychedelic mushrooms even if a person is in a worser state - a complete detach from reality. Again this is risky, never alone, never with inexperienced, uncompassionate people.

Third - supplementary methods. Try getting into that situation from time to time. When your memory is strong enough to be seen and mild enough for you to be in senses try to put a positive feeling into yourself then. You-then feels fear and you-now calms the other you down. This method can be mixed with 1st and 2nd method.

Fourth - if it really gets disturbing and serious like long (few hours, everyday) lasting psychosis try visiting a psychotherapist.

I'd really like to help you and not get moral on you. I don't want to advice you taking anti depressing drugs as they only mask the problem and not solve it. And remember you made it real you can make it unreal.

I hope I helped. Take care !

If your idea of "fun" is taking drugs then you need to seek professional help.