Sometimes, when I wake up after some 7 hours of sleep, I go back to bed and get an OBE-like dream. With this, i mean, i'm lying in bed, feel my body shake, start to listen to a buzz, then I enter a dream, all lucid. I've read that this happens more at the end of the sleep hours (7-8 hours of sleep). Curiously, this past week, I've been experiencing this, right at the beginning, with just 10-15 minutes of sleep. Never happened this way. Why is that?