No it isn't true your spirit leaves your body while you are asleep. Good question, but it involves a long drawn out ceremony to accomplish astral projection, if this what you are meaning. All orifices in the body must be plugged up before accomplishing astral projection so that no other entity can enter your body and take it over.

Aleister Crowley tried to accomplish astral projection many times, but never succeeded.

Tick

I know about the ceremony, but you don't have to plug up all holes, just use a red binding shield, a wax candle usually works drawing a circle on the ground, or you can use an algiez pendent, just make sure its charged...