Narrated Abu Huraira radiallahu anhu:

The Prophet peace be upon him said, "If anyone of you rouses from sleep, he should wash his nose by putting water in it and then blowing it out thrice, because Satan has stayed in the upper part of his nose all the night."

Narrated Abu Huraira radiallahu anhu:

Allah's Messenger peace be upon him said, "If anyone of you performs ablution he should put water in his nose and then blow it out and whoever cleans his private parts with stones should do so with odd numbers. And whoever wakes up from his sleep should wash his hands before putting them in the utensil, because nobody knows where his hands were during sleep."

Shaitan is Jinn made of smoke, or some sort of gases. It’s invisibility also suggests it.

During sleep, the intake of air and its excretion (inhalation and exhalation) are disturbed in some pathological cases and these processes are also even moderated in normal cases such as the nasal cycle. There are many sleep disorders caused due to abnormal breathing known as Sleep disordered breathing.