I've never tried any psychedelic drug IRL, but while dreaming I've taken mushrooms and LSD. (Check out my thread below this one for some interesting thoughts about dream drugs).

I remember one experience (non-lucid), where I took some LSD and then sat at my computer and waited for it to kick in. Then suddenly out of the blue a buzzing, vibrating state of mind kicked me hard in the face everything started moving and becoming more vivid in colour. The experience was so overwhealming that I woke up shortly there after.

I wonder what actually happens in the brain when you take a drug in a dream. Somehow the brain is stimulated even though there is no chemical involved. Weird...