one experiences waves of involuntary shaking and trembling, followed by spontaneous changes in breathing—from tight and shallow to deep and relaxed. These involuntary reactions function, essentially, to discharge the vast energy that, though mobilized to prepare the organism to fight, flee or otherwise self-protect, was not fully executed.
Levine presents trembling as the organism’s primary discharge mechanism for unspent survival energy, a physiological necessity rather than a symptom of pathology.
, In an Unspoken Voice: How the Body Releases Trauma and Restores Goodness, 2010thesis