The freeze response is an opportunity to assess the threat, scan the environment, and prepare for whatever you need to do to survive. It’s different than the flight or fight response, which is a sympathetically driven stress response that results in an increase in heart rate, respiration, and pupil dilation. Freezing, on the other hand, is associated with the slowing of the heart rate and a reduction in body sway. It’s a strange combination of tense muscles and slowing down.
Tonic immobility occurs when an animal “perceives little chance of escaping or winning a fight”. Tonic immobility is like paralysis. It’s when the freeze response lasts longer than is necessary to benefit the situation, or could be thought of as missed opportunity to fight or flee. It’s when the gunman is across the store, distracted by the noise happening far away and you are right next to the door and could get out, but you can’t because you are frozen, unable to change position. Tonic immobility can have long lasting effects, including anxiety and dissociation.
Check out this article about tonic immobility regarding victims of sexual assault: