Not uncommon at all, it sounds like you’re describing the literal “Fever Dream” phenomena, where you have strange and intense dreams and thoughts while asleep and drifting off.
Brilliant! I finally have a term for it. Though, while it does happen more often when I'm sick, it still sometimes happens when I'm not. Maybe I just have a hot-running brain. Anyways, thank you again for an actual term I can search with.