I've had mushroom flashbacks during hypnagogic states. It happens, nothing to worry about.
Are you sure they were flashbacks? Flashbacks are typically triggered by seeing, hearing or smelling a specific thing out of a memory like a bright red boot. During hypnogogic states there is no input.
Also a flashback is not the experience of a type of effects that are reminiscent of a drug's effects. It is reliving one exact experience, virtually always a traumatic one. I get mushroom-like effects during hypnopompic states sometimes and also from cannabis...
But I have only ever had 1 flashback and it was of a trip that actually has been giving me PTSD like problems in my life. During the trip I experience such hellish attacking effects that I did not care anymore if I died instead at some point. Right at that moment I felt like I disappeared and my whole life had been a dream, dreamt by a singularity that also included the dream itself. A sort of deus ex machina dream. It was a zero-dimensional point of being. I stayed in that state for about 4 or 5 hours. When I came down from it and returned to a life I thought had never existed and had been an illusion and lie, for some reason I had the urge to hear a song to "ground" me to that reality. Some detail out of the life to make me remember, to symbolize that all other details would be there as well.
6 months later at a random moment I heard the same song again. For 5 minutes, out of a stone-sober state (there was almost no drug use during all that time that had passed either) I was shot into a vortex that seemed like I was being compressed again into unity, and all colors became extremely fucking bright. It was like remembering a memory I had forgotten and suppressed and living through it from beginning to end after which I was immediately sober again.
Fortunately I felt neutral about having the flashback like being neutral about that most extreme trip of my life. The portion before feeling that neutral however, was easily 100 times better and at the exact same time 100 times more terrifying than anything else in my life. I mean having a very strong trip is one thing but wanting to die, then experiencing a hinduism-like divinity without actually knowing anything about hinduism... that's another thing. And again, it changed me and scarred me for life. But it also felt like it released me, like a blessing.
Since then I felt like there is a big difference between having an experience of 'similarity' and a full blown flashback.
Maybe you had multiple flashbacks, IamMe90... but the seriousness that would imply is not something I wish on you. (Again: my flashback itself was not bad, just the intensity of something that can cause them - originating them - is often unhealthy)