I did an ultra running race that took 37 hours last month. I got maybe 10minutes sleep. I had hallucinated before during (shorter) long races but I had no idea that auditory hallucinations [1] were a thing. it was trippy "hearing" things for a solid 12 hours - mainly off-trail "voices" and the sound of "runners" approaching behind me. No matter how many times I stepped to the side to allow a non-existant runner go by, I kept doing it. It was that realistic
[1] - https://en.wikipedia.org/wiki/Auditory_hallucination