Consciousness is your experience of being awake and aware of yourself and the world around you. Right now, you're conscious of reading these words, of thinking about what they mean, and of being you thinking about them. When you're asleep and not dreaming, you lose consciousness. When you wake up, it returns.

Consciousness is what makes you aware that you exist. You know what it feels like to see the color blue, to taste chocolate, to feel excited about your birthday. Your dog can see and taste and feel things too, but scientists still debate whether animals experience consciousness the way humans do: whether they think about their own thoughts or wonder about their existence.

Consciousness involves knowing you're seeing or hearing things, not merely detecting them. A video camera records images, but it isn't conscious because it doesn't experience anything or know that it exists.

Philosophers and scientists have puzzled over consciousness for centuries. How does the physical brain create the inner experience of being you? Why do you have consciousness at all? These remain some of the deepest mysteries in science. When someone gets knocked out and loses consciousness, they're no longer aware of anything. When they regain consciousness, that awareness floods back, and they feel like themselves again.