Here is a short video that deals with the relationship between the breath and the emotions. In a study, scientists discovered that when emotions are elicited in trial participants, their breathing pattern changes. But the interesting thing is that the opposite thing also happens: When breathing patterns are altered, the corresponding emotion is elicited. Let’s allow Emma Seppälä to explain it:
In the video, she demonstrates the yogic breathing technique known variously as Nadi shodhana or anuloma-viloma. Alternate nostril breathing works just fine, too.