For me, boredom does exist and it comes in the form of extended sensory deprivation. Two days might be doable, but I'm sure that by the end of day one I'd be rather depressed from being forced to face the idea of involuntary confinement. Also, it would depend on whether or not it was a padded cell. If it was padded, I could at least jump around and bounce off of stuff when I got tired of thinking. But a concrete, no-nonsense prison cell would leave me laying in bed all the time wishing the walls were a little less grey and considering doing something crazy just to cause some kind of commotion.