This is obviously just anecdotal, but when I was 6 I got very ill with the flu and was in bed for days. Super high fever and was quite out of it.

I had a, idk, spell one afternoon where I saw this quilt we had on the wall open up at all the squares, and thousands of tiny people/elves poured out. They marched around carrying little boxes and were all around me.

I remember it so vividly more than 30 years later because it freaked me out so much. Tried telling my parents about it and they just dismissed it as a nightmare, but I swear I was awake, just out of it with fever.

Anyways, it was early 90's, and I know I was close to the dangerous temperatures of high fever. Perhaps the brain does interesting hallucinations in these situations?

Have never hallucinated or had anything like that happen since.