I looked up what is this depersonalisation and it does make sense that that is what you are experiencing, as it can be the result of a traumatic experience that it sounds like you had on Siva Ratri with the mind altering drugs.
Depersonalisation is a manifestation of panic, a symptom of severe stress, and it is a well documented result of having had a bad experience on a mind altering drug. You might want to consider that this is a kind of post traumatic stress disorder, (PTSD) and deal with it accordingly, and there are ways you can find some relief from the panic involved without taking any more drugs. One very good method that is free and is considered very effective to treat traumatic stress, is EFT, it is a free and easy technique that might help overcome the responses your subtle body is having.
I cant post a link here, but just do a google search for EFT and you will find more info.
I wanted to just let you know of this technique, you can decide yourself if you think it can help. I was worried about you after reading your post, and I hope it can be of some help to you.
Wishing you all the best
