It's unlikely you wouldn't have noticed this if it were the case but my nose tends to block too by some reason if I lay on my back. What I observed though is th

It's unlikely you wouldn't have noticed this if it were the case but my nose tends to block too by some reason if I lay on my back. What I observed though is that if I lay on a side, there's some mysterious movement about where the sinuses are and one nostril gets unblocked, I think the one facing up (not touching the pillow). If I switch sides, the blocked and unblocked nostrils switch places. So oftentimes I breathe though just one nostril but still beats breathing through the mouth.