I agree with it being Hypnagogia. I've been getting various effects for over 45 years including auditory/visual/sensory hallucinations and other things like Sleep Paralysis which is part of it all.

The hallucinations happen as you transition between being awake and going to sleep (Hypnagogic Hallucinations) and when you go between sleeping and waking (Hypnopompic Hallucinations) you are extremely aware of what's you're seeing/hearing/feeling even if you know it's Hypnagogia it feels so real.

I'm guessing with you being extremely tired enough for a nap and sleeping weirdly on your bed you might have been drifting in and out of sleep and that's exactly when the Hypnagogia occurs. I get it a hell of a lot worse and crazy hallucinations if I nap in daytime as I never go properly to sleep so I'm in a cycle of sleep/hypnagogia/drifting awake/hypnagogia/sleep it's so bad when I nap that I tend to try my best not to and it's something I'm used to for decades. Also if I drink a lot of water/tea before bed I get it a lot in the middle of the night when I get to the stage of needing the toilet and coming half awake aware I need the toilet then drifting back off to sleep then coming half awake again.