Haha, this is what I do. People always get mad at me because they try to talk to me and they think I'm ignoring them,. And when I was a baby, my mum constantly freaked out because I always looked dead. .__.
Well, when you read about the habit of sleep of equines, she would sleep only 3 hours. And standing. But in the case of Celestia which is quite comfortably installed, she can sleep that way. But I agree that with the last thousand year without long sleep (she must have dozed sometimes), she must have got that habit.
Some animals does sleep open eyes. But one at the time for each half of the head. I'm serious there. But with a smile.... she must sleep quite peacefully. Nicely done.