So, that's been something studied at length. And is actually a thing called sensory deprivation. There are rooms built for it that you can pay for to use. The concept is to enhance introspection, supposed to be therapeutic in many ways.
It's also a tactic used in prisons--solitary confinement. Usually only for a few days. It's not sensory-depriving, as it is JUST a room with nothing in it. You're just not allowed to do anything, but you can sing, think, and pick your nails. lol
I think longer periods of time like a month is enough to cause severe depressive disorder. Especially if it is against someone's wishes. Also, the lack of human interaction alone is enough to cause depression if you are not okay being alone extensively.
If you're really interested in answers and more researched hypotheticals, check out cognitive sciences! You'll find a lot in that area of study. See how this would actually affect someone both physiologically and psychologically.