Firstly: interest in treating disease by means of relaxation and breathing exercises only became common among the people after the spread of neuro-linguistic programming and self-development courses. We have previously highlighted the idolatrous foundations on which “vital energy”, “energy meridians” and “out-of-body experiences” and so on are based.
If it turns out that there is some proven medical benefit in breathing in this manner, and that it has a clear physical effect on the body, which doctors know from their experience and research, then there is nothing wrong with the sick person breathing in the manner described and using this as a remedy, especially if this is a way to treat his disease.
But if the doctor is advising that without knowing of any physical benefits based on experience, or he does not know how this kind of breathing affects the body or how it benefits the person who does it, then it is not permissible, because it comes under the heading of imitating the disbelievers without being certain of any beneficial effect.
Shaykh Saalih Aal ash-Shaykh (may Allah preserve him) said:
The one who describes something as a means without any scientific or shar‘i evidence and becomes attached to it is committing minor shirk.
There are some means that lead to results and others that do not.
If the means leads to scientifically-proven results, in the sense that it is something that people know, then we have to see whether Islam allows it or not.
If Islam allows it, then it is permissible to use it,.
If Islam does not allow it, but it is still proven to be effective, such as treating disease with haraam things, in this case we say that it is not permissible.
The third case is that in which there is no shar‘i or scientific evidence for it. In this case, pinning one’s hopes on it is a form of minor shirk.
And Allah knows best.