The last several nights, we've been awakened at 4:30am, every day. By different things, mind you — a cat with a UTI issue, a loud car stereo outside, Beatrix needing a glass of water, that kind of thing.
But 4:30 every day can get pretty wearing. It's not the right time to get up and get things done; no amount of coffee in the world would make me fully functional at that time. But it's also ridiculously hard to get back to sleep; I lay there for often up to two hours, tossing and turning, before I fall back asleep for 30 minutes and have to get up for real and start my day. I have a hard time getting back to sleep when awakened anyway, but be able to sleep through the night the last couple of weeks has been blissful, and coming back to the wake-ups is making me especially zombie-esque.
Kind of analogy for the rest of the day — when can you easily return to something, and when does it take you a long time to get back in the groove?