Hello and welcome!
The first and most important advice is to stop using any hallucinogens and stronger stimulants (amphetamines etc.), since they can make the symptoms temporarily or permanently worse.
To accept that you have HPPD is hard but it is a must. I mean you have to be able to accept a life with it. Personally I´ve had HPPD for nearly 5 years without improvement, but some people have gotten better, usually within a 5 year period. Keep the hope up!
Some HPPD:ers experience partial alleviation of the symptoms from clonazepam, levetiracetam and other GABA-agonists. I have not tried either, but I think you should stay away from clonazepam atleast, since it is a very addictive benzodiazepine. Trading one drug problem for another isn´t the answer, I believe.
I can relate to the fear of becoming psychotic, since I´ve lived with that fear for a long time. But after so much fear, I have not had a single psychotic episode, or anything close to it. I guess that tells how realistic that fear is!
Eat well, sleep well, exercise, talk and hang out with friend/ girlfriends/ relatives, and stay on a good course in life. HPPD isn´t the end of ones life, but it is a turning point. It shows how vunerable a human can be, personally I´ve realized what´s worth living for, and how important it is to not throw the life away on drugs and other reckless behaviour (which I did and regret deeply).
Hope my reply helps!
Take care!