Hehe, yes. Since the literature is split I can offer my anecdata from living in low light conditions (in the mountains of Eastern Europe with no electricity):
It happens rarely. But enough times that one might notice it. If you experiment with lucid dreaming, you realize that the time you usually wake up is in between your REM cycles at the 4 hour mark. If you take a 15 minute break from sleep in your bed at this time, then fall asleep while trying to keep your mind awake (by, say, counting backwards, or just "willing it"), you can fall directly into a lucid dream. If you try this at the beginning of your sleep, you just fall into a long sleep paralysis and hypnagogia session. Your next REM cycle is too far away.
So, yes, it's real. But I think it's more likely that it was experienced much like nowadays, as a rare occurrence rather than a standard.
An interesting data point: even today, the Liturgy of the Hours, which is the regiment of prayer for Christian monks and nuns, contains prayers for the middle of the night.
