How do you know you're not dreaming?

Bizarre things happen in dreams: you fly, or conjure an all-you-can-eat buffet out of thin air, or get chased by witches through the halls of your school. But the strange things that happen in dreams don't seem strange at the time. So, how do you know you're not in a dream right now? Is there a way to prove that you're awake? Daniel Gregory digs into the philosophical theories of wakefulness. [Directed by Daniel Stankler, narrated by Addison Anderson, music by Zing Audio].