Have you ever thought closely about the absurdity of going off to sleep? You enter the world of dreams that may feature people you know or have never met. You go places, experience love or encounter your darkest fears. What's actually going on here?

Five hours, ten hours or somewhere in between - all of us have different relationships to sleep, both when it comes to how much we need it or how highly we prioritize it. Here's a summary of Matthew Walker's book Why We Sleep!