Marijuana changed my brain chemistry from one use?

A few weeks ago I made a mistake by smoking marijuana for the first time. I believe it was called purple haze...big mistake. I got a huge panic attack and felt extremely weightless, light headed, and freaked the hell out!!!! I couldn't feel anything...It felt like i was having a seizure! I used to have them but they are controlled now. So lately, I've been getting head nudges, electric shonock feeling in head, nausea, vomiting. I recently got sick with travels diarrhea...but it seems like it's getting better with the navanic my doctor put me on. I also take ranitidine, carafate, and trileptol. This morning the same happened to me again! I felt very light headed and started vomiting. I couldn't sit down!! I kept pacing back and forth in my apartment!! I had to shower and really force myself to relax!! Even now I'm still getting this weightless, light headed nausea feeling. Please people, I could really use some help if anyone wants to help me. My doctor keeps thinking it's panic attacks but I know it has to be something else! This isn't going away and it's hard for me to live my life this way. I'm a 19 year old male and I've had brain surgery in the past also because of a brain tumor....however, I had a CT scan after the marijuana incident and it came out fine. Idk what damage it did to me..When i stare at something...certain colors strobe in my right eye (A little flashy)....This wasn't happening before the marijuana incident. I really hope it didn't do any permanent damage to my brain... Can someone please help me???? Is this something that will p??? Please some help.... God bless!