I usually have long streaks of sleep, but sometimes in them, I'll wake before I completely finish my sleep schedule. Sometimes I have trouble getting back to sleep, and when I do, it's impossible to fall back to sleep. Sometimes even if I'm asleep for 4 hours, I'll feel like I've been sleeping for 12, and will proceed to be tired the rest of the day. Can I ensure that I'll fall back to sleep, even at the end of a sleep cycle?