Kundalini Yoga is a specific, doctrine driven, tradition. The awakening energy located at the base of the spine is to be freed by meditative yoga to pass through the cakras until it breaks free into awakening and union (yoga means union) with God. But yoga practices are used by a great number of Asian traditions, where is is simply the seated posture for meditation and prayer. And the there is yoga at the YMCA, which are just stretching exercises. In Buddhist practice any demons are internal obstructions - fear of death, impermanence, etc. Which is why speaking about yoga as a simple "thing" is mistaken.