Sweet Dreams

In a world where life continuously competes for resources, one would think that sleeping would have made living beings more vulnerable and at high risk of predators, and yet, nature decided that there was a strong evolutionary advantage to putting living beings under that spell. Why? What's the secret? Dreams are a strange realm that requires further exploration.

Add books you've read that feature a scene where a character is sleeping and/or dreaming, or books you've read that discuss sleep and dreams.