Headstand (Sirshasana) is really a blessing and a nectar. Words will fail to adequately describe its beneficial results and effects. In this Asana alone, the brain can draw plenty of Prana (vital life force) and blood. This acts against the force of gravity and draws and abundance of blood from the heart. Memory increases admirably. Lawyers, occultists and thinkers will highly appreciate this Asana. This leads to natural Pranayama (Breathing Exercise) and Samadhi (Superconscious state) by itself. No other effort is necessary. If you watch the breath, you will notice that it becomes finer and finer. In the beginning of the practice, there will be slight difficulty in breathing. As you advance in practice, this vanishes entirely. You will find real pleasure, exhilaration of spirit, in this Asana.
Yoga Asanas By Swami Sivananda (A Divine Life Society Publication)