Yoga is based on ORIGINALLY Hinduism. The yoga that the average North American does is a far cry from the spiritual awakening yoga that a Hindu will be doing.
In Hinduism, all things are God or are capable of being God. (Namaste meaning:I see the divinity in you.) Hindus believe that Yoga is a physical means of bringing spiritual energy through the chakras (energy centers of the body that control different areas), up to the Ajna (or Third Eye) where this energy can be used to help your consciousness leave the body and experience other realms, bringing the person closer to their Divinity. There's also a part to it called Kundalini, but that's a long story....
Anyhow, North American yoga is far removed from what the Hindus mean it for. Here, it is a physical stretching exercise and sometimes there will be a meditation component at the end.
It's not dangerous, spiritually. It's all about intention.
I hope I explained that well enough. If anyone has anything to add or to correct, please do so.
Watson