These practices are not only pleasant. They change things you could measure, which is worth knowing on the days when pleasant is not reason enough to bother.
Yoga and breath work tend to get filed under relaxation, and that undersells them. There are claims made about them shifting the chemistry involved in attention and impulse control, and about sleep, mood and blood sugar too. Some of that stands on firmer ground than the rest. The dependable core is that slow breathing measurably changes how the nervous system is running, and that is a physical effect rather than a mood.
Qur’an and Sunnah
He gave you hearing, sight, and minds (Quran 32:9). The body and its faculties are spoken of as real things given to you, so tending them is not a lesser sort of care.
ثُمَّ سَوَّىٰهُ وَنَفَخَ فِيهِ مِن رُّوحِهِۦۖ وَجَعَلَ لَكُمُ ٱلسَّمۡعَ وَٱلۡأَبۡصَٰرَ وَٱلۡأَفۡـِٔدَةَۚ قَلِيلࣰ ا مَّا تَشۡكُرُونَ
Then He moulded him; He breathed from His Spirit into him; He gave you hearing, sight, and minds. How seldom you are grateful
Qur’an 32:9read it in the library
Translation: M.A.S. Abdel Haleem, The Qur'an, Oxford University Press, 2004.
What the research says
In young adults with slightly raised blood pressure, heart rate variability biofeedback lowered blood pressure and improved baroreflex sensitivity, which points to slow breathing changing autonomic function rather than only felt calm. That is one condition and one form of training. The wider claims about brain chemistry sit outside what these studies looked at, so hold those more lightly than the physiological ones.
Lin G, Xiang Q, Fu X, Wang S, Wang S, Chen S, Shao L, Zhao Y, Wang T. (2012). Heart rate variability biofeedback decreases blood pressure in prehypertensive subjects by improving autonomic function and baroreflex.. Journal of alternative and complementary medicine (New York, N.Y.) doi
Strength of evidence: one line of research. A single study, or a theoretical account.
Why it works
A practice that alters your physiology is still working on the days it does not feel like anything.
This one is still a draft. It is waiting on a scholar and a clinician to read it before it is published.
Near this one
To find the soft ocean sounding breath, breathe out through your mouth as if fogging up a mirror. Then keep that same slight narrowing at the throat with your mouth closed, and let the sound get quieter and quieter.
The rapid belly driven breath with pauses added is the strongest thing in this set. Not for high blood pressure, glaucoma, pregnancy or your period, and stop at once with pain or dizziness.
Fighting, running and freezing are the ones everybody can name. There is a fourth: going along with things, smoothing them over, making yourself easy to be around so that nothing bad happens.