[djur]

1) People who are not fully awake often do things for no clear reason -- I regularly wake up finding that I have no memory of removing my mask after 2-5 hours.

2) If you're prone to nightmares, waking up with something covering your face that causes bizarre sensations when you try to breathe through your mouth or speak may disturb you enough to tear it off.

[Suppafly]

I pretty regularly take my socks off while sleeping and occasionally take my pants off, no way is my sleeping self not going to take a mask off.