Any halucinogenic drug. Refers to the halucinations you experience while under the influence of halucinogens, as they can be like dream, but in a conscious state.

Also a song by the band "At The Drive-In".
Dude1: Hey, you're acting kinda wierd, man.
Dude2: You know that last tab of acid I was saving?
Dude1: Yeah?
Dude2: I dropped it.
Dude1: Far out, man. You took a sleepwalk capsule?
by Crapper McGee March 28, 2004
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