I happened to be sick on the morning the ACT. I had a fever and was unnaturally tired. When I got home I fell asleep and couldn't wake up for three hours.

On the math section I would typically have gotten a 36, but it was the section least affected overall.

I was actively fighting to stay awake during the reading section, usually I score around a 34 on the practice tests though.

Science was completely unexpected tbh.

ENGLISH however... my English practice tests varied from around 28-33 in score before I studied. It was the only section I studied because quite simply I've had a really bad history with English teachers. I studied it about a week beforehand and focused on grammar stuff, but it would appear that being sick doesn't help recover newly formed memory.

Moral of the story- don't be sick and study early