I just read about sleep paralysis for a bit. It sounds very much like what my problem might be. I didn't realize it until you said it, but I can't move when I see these hallucinations, but as soon as I sit upright, reality sets back in. Thank you.
Try looking up Sleep Paralysis. (of course this would mean while you saw these visions, that you could not move.
as soon as you move they would then vanish. but yeah, if that makes sense. Look it up.-
If you have any symptoms of sleep apnea, you may want to consider a sleep study. I have a friend who hallucinated much as you describe, and it turned out to be due to low oxygen during apnea events. Maybe you should talk to your doctor about it.