Short answers, pulled from the story.
Experiential avoidance describes attempts to avoid thoughts, feelings, memories, physical sensations, and other internal experiences. This process often creates harm in the long run even when it seems helpful initially.
Major depressive disorder manifests through isolation or suicide targeting feelings of sadness and guilt while posttraumatic stress disorder involves avoiding trauma reminders. Social phobia drives individuals away from social situations due to anxiety about judgment from others and panic disorder causes avoidance of situations that might induce panic alongside fear of physiological sensations.
Laboratory-based thought suppression studies suggest avoidance is paradoxical in nature because concerted attempts at suppression of a particular thought often leads to an increase of that thought. Studies examining emotional suppression and pain suppression indicate avoidance is ineffective in the long run as sustained effort to suppress specific mental content backfires consistently across experiments.
The Acceptance and Action Questionnaire was the first self-report measure explicitly designed to measure experiential avoidance before being re-conceptualized as a measure of psychological flexibility instead. The Brief Experiential Avoidance Questionnaire is a 15-item measure using MEAQ items and has become the most widely used measure of experiential avoidance in research settings.