I highly doubt Chakra or Ki exists - that is merely occult philosophy (of an Eastern kind as opposed to Western Esotericism, but a lot of the philosophy is similar.) Ki is the rough equivalent of the life energy the western occultists I quoted talk about and Chakra has a lot to with the Caduceus in western occultism. The goal of Yoga, in the Eastern context, is to make the person spiritual passive so that the yogi may obtain power by becoming possessed by the Kundalini spirit (a demon.) I don't believe these energies actually exist, but the practice of yoga does exist because it has effects on people. I don't doubt that demonic possession is a possible result of yoga.
"While such experiences are typically labeled pathological by Western clinicians, they can be identified as part of spiritual awakening in Eastern meditative traditions." In some way, it is likely that yoga exists as an occult system for the purposes of producing psychotic episodes (i.e. a religious experience.) A Yogi would say the psychotic episode is the chakra opening. One of the possible delusions that result is the delusion of power, but it doesn't mean there is reality behind the delusion.
edit: here is a link
Is Bikram Yoga Safe?
Hot Yoga: Is It Super-Heated Exercise or a Health Danger?
The cause of these illness are scientifically explained, nothing involving magic, occult, or whatever.
Yoga works, from a Christian perspective, by disassociating the soul and body through placing the body into unnatural positions - leading to delusion.
Here is a credible scientific article about yoga induced psychosis.
Psychiatry Online