Stress is the biological activation of the fight, flight, and freeze response. Stress can be beneficial when it supports you in taking needed actions throughout the day. However, you need relief from this active state for stress to remain beneficial. This process is akin to the inhale and the exhale; we need both. If we only inhale and never experience an exhale, we could not breathe, and our system would not function.
Stress can become traumatic when you are constantly in a fight-flight-freeze activation. For example, when you are in a flight state, you might have impulses to leave a job or a relationship. You might feel as though you need to move homes or radically change your life situation. Flight is the experience of anxiety. When you are in a fight state, you find yourself irritable over little things. You might feel aggressively toward those close to you. You may be more confrontational than usual, or you may turn your anger inward through a loud inner critic. When you are in a freeze-state, this is the experience of depression.
When stress is not discharged, it can build in your nervous system. And, when enough stress accumulates, you may experience symptoms of trauma. Trauma is stress that is so significant that it can cause co-morbid disorders like anxiety, depression, and addiction. Genetic factors may also play a role in the development of depression. Although there is still much to be researched here, twin studies, linkage studies, and association studies explore how our environment and genetics can potentially lead to a greater risk of developing depression.