Sighing – to regain one's standing
When a person prays with divaikus (binding, clinging to Gd) or does hisbodidus properly, and in the middle he falls from his level, this stems from defection of (the) faith, and so it is necessary then to break his heart inside, and to be ashamed of himself for falling from heaven to earth, and he should pity himself until he sighs, and through the sigh he will return to his level.
Na Nach Nachma Nachman MayUman
(Likutay Moharan, torah 108; Outpouring of the Soul 63)