The breathing has been used throughout centuries in many many different cultures as one of the most powerfull means to change consciousness in many different ways.
You can do all kinds of things with your breathing to change your consciousness. Some of those ways are very extreme. For example the original baptism as it was practiced by the essenes, involved actually four or five people taking the initiates to the river and holding their head under water until they came close to death and then surficing them.
You can change your conciousness by breathing faster, by witholding breath or alternating those two. And there are also very refined very suttle ways of changing conciousness with breathing where there is no change in the actual rate of breathing but there is a certain quality of attention to the breathing.
Like in the eastern spiritual traditions. In zen for example you just pay very exclusiv attention to your exhalation or to your inhalation. They are also in many of the aboroginal traditions. Either breathing or certain vocal performances that change breathing are used to alter conciousness. The eskimo Inuit throat music, the Monkey chant in Bali and so on.
Stan Grof has experimented in his workshops with many different ways of changing conciousness by breathing and they have found out that is very simple. All you have to do is to ask people to breathe a little faster, little deeper with this quality of attention where you shift the attention from your head, from the cognitive proces to your body, to your breathing. After while that profoundly changes consciousness.
What they see is in many instances a development of tensions in different parts of the body. In the medical literature you find the concept of the so called hyperventilation syndrom – the idea is that when the people breath faster they develop spasm in the hands and in the feed this is called carpopedal spasm in the medical literature. And they also get agitated and a lot of powerful emotions come up and there is a tendency to see it as a kind of undesirable thing in medicine and various ways are recommended how we can stop it.
Stan Grof has done the work with 25 thousand people and he sees that its simply a myth in the medical literature. Many people who breathe will actually go directly into a very profoundly relaxed state. The more they breathe the more relaxed they feel, they start seeing the light and they feel connected to other people, to nature and they have just a beautiful experience.
But most people would develop some form of tension in their body but it doesnt have to be in the hands or in the feet. It could be anywhere in the body. The way we understand it now is that the breathing creates a condition in the organism that certain old tensions that are associated with traumatic situations (biographical, birth experience and so on or even something coming from transpersonal levels). These deep tensions start surfacing and their manifest. And actually by experiencing them people are getting rid of them.
Source: Stanislav Grof (YouTube video – Stanislav Grof: Holotropic Bodywork Workshop [Part 1])