freeze, causing inaction.
A genuinely overwhelming and paralysing freeze response is thought to occur when neither fight or flight is available to you. That is, you have been so overpowered, overwhelmed or trapped, there is no option to either flee or fight.
Given our evolutionary history this probably occurred most often during hunting (the sabre-tooth tiger has the better of you and there’s just no way out). So we do what a number of animals will, we “play dead”.
The biology of fear- and anxiety-related behaviors – Thierry Steimer, PhD*
According to Panksepp, flight and other active coping behaviors are unconditional responses to proximate threat, whereas passive coping strategies, such as freezing, are conditioned responses to [external] stimuli predictive of danger. These two strategies have distinct and successive roles, and are modulated by the (cognitive) apprehension of the environment and probability of success, eg, whether or not there is a route of escape. Thus, when an animal faces a predator, freezing is preferentially activated when the source of known danger is still far away. When danger gets closer, and the stimulus passes through some critical “psychometric” distance, it becomes a true unconditional stimulus and a flight pattern is activated.