I read a study done a couple years ago in Switzerland about sleep and cannabis. Apparently THC inhibts REM sleep (you know, dreaming). This means that a person with THC acting upon their brain won't enter REM sleep until the THC has been completely absorbed, usually early in the morning. That's why most people who go to bed stoned, myself included, don't remember having many dreams, except when they haven't smoked for a day or two. Then there is a sudden rash of bizzare dreams.

Peas out