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 establishes involuntary discharge — manifest as trembling, shaking, and altered breathing — as the organism’s primary mechanism for releasing survival energy that was mobilized but never consummated in defensive action.
, In an Unspoken Voice: How the Body Releases Trauma and Restores Goodness, 2010thesis