The same exact thing happens to me!
It never works when I'm with friends because we're usually doing something, but when I'm alone and toke up, I lay back, have my eyes just resting half open not completely closed, and just start to focus on the music playing or life in general. It gets to a point where my body can't control itself and starts waving side to side on its own... it's the best feeling in the world. But when I open my eyes normally or drift away from focus the feeling sort of "jolts" out of my body and I become sober (well not SOBER, :jointsmile.

Ahhhhhh I praise you marijuana