i do this as well. the first time i noticed this was 5 years ago when i was a "rookie" at getting stoned and i smoked up and was in my buddy's basement went on windows media player and listened to the song "flying in a blue dream" by Joe Satriani

at first my eyes were open and i watched the visualization in WMP, eventualyl my eyes closed but i still saw the visuals, in fact i saw them more clearly and its like i got sucked into them and it became all around me i was the particle of energy controleld by the lead note of the guitar and i was moving throguh warp tunnells in which the walls were changing scenerey that seemed to cometpely real that would change according to the sound of the note/sound of the lead guitar...i was literally flying in a blue dream

it was amazing, ive been donig it ever since with all kinds of music

most music will give you this effect, just some better than others - you just gotta sit and relax compeltely think about nothing and lay down or something close your eyes or not it works either way