What would happen to a person if they were deprived of any sort of entertainment for days?

Okay, first off, let me explain now that I am a WRITER. Not a psychopath or something, hehe.

Secondly, let me elaborate a little bit:

If someone was kept in a plain, white cell with no means of entertainment whatsoever besides a small window that looks out into space (the thing I'm writing is a Doctor Who thing) for several days, what would happen to them? Like, psychologically and behaviorally? And how would they behave when they were let out of the cell? Would they be spacey? Easily overwhelmed? Neurotic?

I have a character who's being held hostage (also in danger of possibly being executed) by some villains in an empty, white cell, being fed by means of a sort of nutritious aerosol sprayed into the room at certain times of day. Not sure that last part's actually possible, but what the hell. Eheh.

So yeah, how would their behavior and psychological well-being be affected by something like this? Keeping in mind that the aforementioned character has been through some other intense/traumatizing experiences already and is slightly accustomed to dangerous situations, and they've been rescued by their counterpart every time.

Thanks! c:

(sorry, wasn't sure about the category)