How do you know you exist?

How do you know you exist? What tells you that you are real? Is existence all just one big dream? Has some mad scientist duped us into simply believing that we exist? Are we part of a computer simulation being run by humans of the future in a world we have already created?

Phew! A lot of big questions for a morning! Take a look at this short Ted-Ed video to help kick-start some of the thinking trails.