Stage 1 - Feeling something. This happens to Mom when she takes a double dose of nyquil in the winter.
Stage 2 - Feeling high and trippy, walking outside is fun, music seems to warp in time. Body feels like jello. Great for the common man.
Stage 3 - Heavy dissociation. Walking is barely possible. Strong out of body waves. Mind is completely twisted. Strong open eye visuals, bodily sensations heavily distorted. ESP Phenomena possible. This is usually the aim for those who want a good trip.
Stage 4 - Complete dissociation. Full on extra sensory attainment, complete adhesion to the fountain of wisdom. Complete out of body experience, total lack of awareness of surroundings. Inability to function, speak, or move. This is usually a product of taking too much and accidentally seeping into sheer madness.