For serious depression issues, I'm not sure 'abuse' is appropriate here...
The inability to _want_ to do anything or _care_ often isn't a conscious choice.
Not to mention that depression often makes people feel physically tired all the time. I don't think someone with normal neurochemistry even could sleep 16 hours a day if they wanted to.
"Abuse" is Newspeak, it means "abnormal use". When depression causes you to sleep to avoid life situations, it could even be called addiction.
That's precisely what I meant in my edit
Or...uses sleep to reduce the inflammation of the brain, thus treating (the symptoms of?) depression?