Pratyahara is the withdrawal of senses from all external objects. When this is done, the person no longer perceives external objects of any sort. This process of withdrawal involves unraveling the sight, hearing and senses from the way one naturally looks at things i.e, with a sense of attachment or aversion. This can be attained by the power of judgment which divests the senses from unworthy thoughts (considered as nourishments) and masters every movement of the mind. Hence, on the whole, Pratyahara in Ashtanga Yoga means withdrawing one-self from things that nourish the senses.
Withdrawal takes place when there is an interruption in the activity of mind. It means our senses and mind stops depending on objects that stimulate them or feed them. In the concept of Pratyahara, the senses remain unaffected or uninfluenced even if the most attractive objects are spread before the senses. In other words, the brain disregards all that is received by other sense organs and learns to accept and work on only the signals sent by the brain. On attaining this stage, an individual will gain better control over his senses rather than the senses controlling the individual.
When one is completely focused on breathing during Pranayama, the occurrence of Pratyahara takes place automatically. All the senses are automatically drawn to the mind, which in turn is focused on the breath. Pratyahara should not be mistaken as a state of sleepiness. Rather, it is a state in which one is very much alert and is capable of responding, but the senses do not respond as they are kept detached from external world.