Clear your mind, dont think of any worries or important things. Go to the bathroom, shut the lights off. Needs to be completely dark, no lights or noises in the room.
Open up your shower and go sit under warm water. Then start staring at darkness and listen the shower wash. Wait few minutes and you start seeing colours, maybe hearing voices and other creepy shit.
This is psychological thing and tricks your mind. See more at http://en.wikipedia.org/wiki/Sensory_dep rivation
I just tried this and it is probably the freakiest fucking thing, ever.