5 month old overheats while falling asleep?

Mikko • Single mom, tattooed, pierced, 日本語OK, sto imparando italiano.

So just these last few days DS will fall asleep in my arms but starts to get really hot, sweaty even. Which obviously makes him uncomfortable and harder to fall asleep. I’m not sure what’s going on. The temperature in the room is okay at 20C (68F). I’ve lowered it since to 18C (65F) but he’s still so hot. He eats and poops properly, and his body temperature is normal.

Any mommies (or daddies) know what’s going on?