I've also experienced psychosis DURING one trip, and that's fairly common even for people who don't otherwise have psychotic tendencies. As soon as I came back down, I was fine.
... I think?
Unless this whole world really WAS a trick to distract me from an unbearable solipsistic loneliness, and eating two grams of mushrooms really WAS what I needed to remember?!
You were tripping, thats not psychosis. If that lasted well beyond your trip and use of any other drugs you may be able to call it psychosis. I dont think psychedelics can cause permanent psychosis in healthy individuals. Its def possible to experience disconnect for a while after a bad trip. If you are healthy it wil not last forever. It can also bring out preexisting problems in people who are not mentally healthy from the beginning.
You can def lose your connection with reality from using psychedelics. It is only true psychosis when it doesn't do away even after stopping using drugs. From what i understand using strong stimulants in combination with psychedelics is a fast road to big problems of this sort.
I think it's generally agreed that they can catalyze the development of mental illnesses that would have developed anyway.