To kill oneself you need to do something detrimental, which is harmful to the body, damaging to the body.
For your example of using pills to sleep forever, use Violence defintion number 2: a detrimental treatment.
The mind/body separation is a false dichotomy.
I am my body. You are your body.
If one's life has consisted of more suffering than pleasure, suicide is NOT detrimental to oneself, but a mercy.
Death is also a mercy when you're absolutely certain your future will consist of more suffering than pleasure, as was the case with Aaron Swartz, the brilliant young computer scientist who hung himself to avoid decades in federal prison. See my signature for links.