Question: Does Vader sleep in his suit?
Answer: Darth Vader does have his own personal chamber made to assist him with the equipment /suit he wears as well as, I'm sure, for resting/meditation purposes. Also keep in mind that Jedi/Sith, especially those trained to use the force (particularly those having mastered it), don't need the same sleep requirements regular folks need. They can "sleep" sitting straight up, on top of much harder elements and they can even "draw" energy from the force to help them stay awake. The expanded universe, via the books, gives more examples of Jedi/Sith sleeping or measures they take.
Answer: Darth Vader has a special chamber in which parts of the suit can be removed for comfort. When he is not in the chamber he must wear it at all times in order to survive.