In my Taiwanese teacher's system of qigong, all the exercises can be broken into levels. As they move from the third to fourth level they become much less physical and more mental/esoteric. Apparently if you meditate while the qi is flowing strongly enough you will start to feel sensations of wind, clouds, water, fire... and these will change your perception of things in life (note, I haven't reached this level at all, so I'm just reporting what I heard here).
My teacher said after you reach this level it also becomes possible for the mind to leave the body (aka astral projection), but that it can be frightening and potentially dangerous if your body is disturbed while you are not in it... It sounds kind of "out there" to me, but then I've learned to keep an open mind about what is possible with qigong.
What senses do we lack that we cannot see or hear another world all around us?
--The Orange Catholic Bible