Hello Btown: I see this is your first post here on PC. So welcome to PsychCentral. I'm afraid I can't really tell you a whole lot about this. I have no personal experience with the use of the types of drugs you describe. The only thing I can say is that, from reading posts here on PC, I have the impression the type of drug use you describe can really mess up a person's mental processes. Drugs don't simply disappear from a person's system, once he stops taking them, leaving it the way it was before he started. They have a lasting impact on the functioning of the person's brain.

Over time, your friend's brain became adapted to functioning with these drugs in his system. Now that he is no longer using them, his brain is having to go on functioning without them & it's not functioning well. My impression is this is not unexpected. From my non-professional perspective, you may well be right to be concerned for your friend's safety as well as your own. And, unfortunately, there's likely little or nothing you can do about this beyond encouraging your friend to seek the professional medical / mental health care he needs. Beyond that, I would suggest the most important thing for you to do here is to take whatever steps are necessary to protect yourself.
I wish you well...