A couple times in the 70s when I took LSD. First experience was during a party, visual light trails from a lit sig, everything in the room color enhanced just by thinking of any color, music experience was enhanced.
The second tme was more of a spiritual experience, feelling that I was connected to everything else in the universe, realization of just how small I was in the universe, ego was gone and I became fully aware of the pain I caused others in the past by my actions.
One other time I had the feeling that someone was pushing me from behind, but no one was there, I was walking into my house alone when it happened. That was a bit scary compared to other experiences and I wanted to think it was all in my mind but at the time also felt like it could have been a demon pushing me. I never did anymore again after that and I never experienced any flash backs.
My father had many hallucinations when he was on strong pain meds and would just lay awake in his bed with nothing to stimulate his mind. Once we talked him into keeping the TV turned on or doing things to keep his mind active instead of idle while awake they seemed to go away. He would see things like the numbers and hands of the clock falling off onto the floor and chrickets jumping up and down on his bed about 3ft into the air.
Had one audible hallucination shortly after my mother died, I heard her voice just as clear as if she was standing right next to me. I was in bed at the time just falling asleep. No drugs were taken.