When your fight or flight system engages, holding it in can leave that energy trapped in your body.
Getting up, moving and expending that energy can help release the build up of tension.
Exercise
One simple way to expend energy is physical exercise.
Lift some weights. Do jumping jacks. Run in place. Go for a brisk walk, bike ride, jog or run.
In addition to engaging your fight or flight reflex in a productive and healthy way, activity such as walking may also be the added benefit of bilateral stimulation that comes with repeated, alternating motions of both sides of your body. Bilateral stimulation is what makes EMDR therapy work, and may also help to neurobiologically process emotions while you exercise, dance or do other activities that involve the left and right parts of your body.
Shaking
Scientists who have studied tonic immobility (the “play dead” or freeze response) in animals have learned that some animals will shake when coming out of that state.
It is not so different from a person who becomes stuck when challenged with an impossible situation. If you are connecting with your feelings and find yourself wanting to shake or tremble, there’s nothing to be ashamed or afraid of. It’s your natural instinct to release and burn off the energy of the trauma so you can re-enter and engage with life again.