Re: Sleeping on the Enterprise
There probably is a watch officer that takes over when the regular command crew goes off-duty. He or she will not be qualified to really command the ship, but qualified enough to supervise its normal operation. Whenever there is an emergency or some other situation that goes beyond the capabilites of the watch officer, the captain can be called to the bridge at short notice. AFAIK this is the way it was/is handled in our real-life navies.
"Do you give me attitude, Spock?" - "I´m expressing multiple attitudes simultaneously, Sir. To which are you referring?"