Kapalbhati and Anulom Vilom pranayama can be bad for some people, especially to those who have a damaged nervous system already. Some people face diarrhea because of over-doing it as they generate a lot of heat in the body. Don't try to practice this too much if your are a beginner. These people are telling people to do Kapalbhati and Anulom Vilom for as long as 15 mins and 30 mins, which can be dangerous. Dont overdo without proper training and practice. Hatha Yoga is safe, but not pranayamas. Learn Pranayam or any breathing technique from a qualified teacher rather than from a DVD.