Explain what is meant by the term olfactory fatigue or olfactory exhaustion.

This is the temporary inability to distinguish a particular odor after a prolonged exposure to that airborne compound. By the way, don't copy that word-for-word because I just got that off of Google :)

Probably because you wake up early. even when i get a good nights sleep i still feel tired if i wake up early. or maybe you just need coffee.