Daniel Pierce: Reality is a figment of your imagination. Who here hasn't woken up breathless from a nightmare and thought 'oh thank God it's just a dream'? That's because neurochemical impulses fire when we're dreaming or fantasizing or hallucinating are indistinguishable from the one's banging around inside our skulls when we actually experience those events. So... if what we perceive is often wrong, how can we ever know what's real? And what isn't.