I could imagine what it might be like. You go in after trial, your mind still busy with all the crime you did or whatever you are thinking about, and the cell door finally shuts behind you. You are still the same guy who was outside just a few hours ago, and you've been many places for only a few hours, so this feels no different.
Eventually, after days, weeks and even months, the realization that you aren't leaving sets in, and you slowly give up hope that somehow, some way you will get your freedom back. Not this time though. The best years of what was supposed to be your life out there, are going to be spent in here.