Actually, it depends on how narrowly you define “meditation”.
Clearly, if you see meditation as exercising a certain technique, like focusing on the breath, then that’s going to be incompatible with sleeping. But there’s a more inclusive way of understanding meditation: as a surrender to what is, giving one’s self over fully to life as it unfolds. Seated on the meditation cushion, this may mean giving yourself over to the experience of the breath, but at bedtime, it means giving yourself over to sleep. Sleep just happens to be a form of meditation that most of us have little trouble with. It’s the waking forms that give us a hard time. The formal, technical kinds of meditation are really just ways of training the mind for this more inclusive meditation.
There’s an anecdote from the history of Zen that bears on this. The head monk at a temple found a certain monk napping in the middle of the day (this napping monk had already shown a certain prowess in meditation, by the way). The head monk started to scold the napper, but the master of the temple stopped him and said, “Why do you disturb this monk in his deep meditation?”
What most of us need to work on is the tricky business of single-minded absorption in our waking activities, so we’ve developed these techniques to help us with that. But sleep is another expression of single-minded absorption. Meditation has to eventually be seen in this most inclusive sense, as being something that is seamless through the 24 hours.