A yogi is someone who practices Yoga. A yogin is a male Yoga student, a yogini a female student. A guru is a teacher. "Swami" is a title of respect for a spiritual master. I just have started yoga practice, but I feel drowsy all through the day. Yes in several cases it happens. One may feel uneasy for one to two weeks after starting the practice of asanas. It may happen because the yoga exercises cause the body to release deep rooted toxins, this toxins when comes to the surface, it spends some time in the blood before being eliminated. After this initial phase of body clean-up, you will start to feel much better. The more toxins you have, worse you will feel in the beginning.