Is it possible for drugs to cause PTSD from a bad experience?

Ever since taking DXM Coricidin Cough and Cold and having a bad trip the second time I tried it, I've thought that it somehow damaged my brain. They say that it never causes brain damage in short term use, only long term. I only took it twice, the first time was good, so I did it again, and smoked weed with it, and I had a very bad time. Also the next night I smoked weed and I felt the bad trip all over again. After that I started to get anxiety problems, and every time I would smoke weed I would trip out exactly like I did when I took the CCC's. It's been a year and all the anxiety and panic has gotten worse. One thing that is true about it is that 90% of my anxiety and panic happens when I smoke weed, or take any kind of drug, including, ADD meds, and I had a mild panic attack the first time I took Xanax, until it kicked in, lol. I have recently quit all drugs, ( I didn't take many before, just smoked weed, and like to experiment sometimes) which is hard because I'm in college. But hopefully long term complete sobriety will help. Does anyone think this could be post traumatic stress disorder? Does anyone think it couldn't be?