Is it dangerous to practice Pranayam without the assistance of a Guru or teacher?

You can practice ordinary Pranayam exercises without the help of a Guru. There is no danger in practicing Pranayam, Asan, etc., if you are careful, if you use your common-sense. People are unnecessarily alarmed. There is danger in everything if you are careless. If you are careless in getting down the steps of a staircase, you will fall down and break your legs. If you are careless when you walk in the busy parts of a city, you will be crushed by the motor-cars. If you are careless when you purchase a ticket at the railway station, you will lose your money-purse. If you are careless in dispensing mixtures, you will kill the patients by giving a poison or a wrong medicine or by administering a medicine in over-doses. Even so, when you practice Pranayam, you will have to be careful about your diet. You should avoid over-loading, you should take light, easily digestible and nutritious food. You should be moderate in copulation. You should not go beyond your capacity in retaining the breath. You should first practice inhalation and exhalation only (without retention of breath) for one or two months. You should gradually increase the ratio from 1:4:2 to 16:64:32. You should exhale very very slowly. If these rules are observed, there is no danger at all in the practice of Pranayam.

Swami Sivananad