I have excessive yawning sometimes. Other times I try to yawn but it doesn't work somehow. The inhale part of the yawn happens but then he exhale doesn't feel like it's doing anything, ie, not clearing out carbon dioxide etc. It's kind of annoying.
I largely stopped yawning when i developed ME (acute viral onset). Stopped sweating about 10 years into the disease. The hot flushes that I get seem to be related to low BP.