This is an experience that typically involves a sensation of floating outside one's body. 

Falling asleep physically without losing awareness. The "Mind Awake, Body Asleep" state is widely suggested as a cause of OBEs, voluntary and otherwise. 

Writers within the fields of parapsychology and occultism have written that OBEs are not psychological and that a soul, spirit or subtle body can detach itself out of the body and visit distant locations. 

Indian Hypnosis Academy, 
The Center of Clinical Hypnotherapy & Advance Hypnotic Sciences.