Or put carpets on the walls and wallpaper on the ceiling and systemboard on the floor.
Haha okay both not too realistic I guess... I would probably get some wacky colors and perhaps fluorescent and/or glow in the dark paint and make some sick psy art.
When I was young but over 6 (my parents divorced when I was 6) my entire bedroom walls at my dad's place were covered in bullshit I put on there with black marker. Some drawings, some jokey stuff, graffiti tags (a piece at my mother's) etc. Not psychedelic really but when I think about it now thats how they depict the room of a madman on the screen dont they?
Oh what is also cool is a lamp with a rotating cylindrical shade around it, a cutout with holes with special forms that you spin on a record player I guess. I forgot the name of the device but if you sit in front of it it's supposed to alter your state of consciousness...