The late Dr. Milton Erickson, a renowned psychiatrist and major innovator in terms of modern hypnotherapeutic theories and practices, once proposed that all learning is acquired in a form of trance. The conscious and unconscious minds align into a state of receptivity and thus of increased suggestibility, ready to accept the incoming information or experience as Fact and Truth. Thus, the sense of mental expansion felt during periods of intense focus while acquiring or applying knowledge, referred to commonly in pop culture as "the zone," is actually a type of waking hypnoidal trance. This theory is put into practice as an explanation for the efficacy of some encounters over others in forming lasting imprints, and to effectively address events within the memory by accessing the remembered trance state during which they were formed or reinforced. There are other, less deliberate conditions capable of inducing a similar selective focus, even contributing to hypersuggestibility (one of the goals of most hypnotic trance). Applications of extreme emotion, positive or negative, or adrenaline are especially effective.
Fear and trauma are a prime combination, snapping the mind into ultra-constricted awareness and attention to specific aspects of the given situation. Personal testimony provided by survivors of terrible events often include comments about how some small feature, perhaps even counter-intuitively and difficult to consciously reconcile after-the-fact, takes on increased significance disproportionate to other factors (try searching the web for "I just remember," quotes included). Beneath this conscious awareness, the sub-conscious performs similar singular attachment. The results of this extreme focus creates new triggers for the remembered trauma, and seemingly ordinary settings or items can reproduce the original emotional state and responses (one of the most disruptive conditions of flashbacks and Post-Traumatic Stress Disorder). The victim/subject of this experience will be unable to "let go" or become selectively unaware of the triggers, and the gut-wrenching realism of the recall causes enough distress as to interfere with daily living, as well as essentially reinforcing the response to the original stimuli in a self-perpetuating pattern.
Interestingly enough, the sub-conscious mind thinks it's doing a favor by initiating and exercising these connections.
One of the primary duties of the sub-conscious is protection of mental, physical, and emotional wellbeing. Its perceptions of what constitutes a threat do not necessarily agree with conscious opinion of the same, hence the seeming irrationality of many phobias and some behavioral disorders. Methods used for protection from the evaluated threat can similarly be at odds, capable of producing responses which one would not otherwise agree with. My old hypnotherapy mentor's materials included a case study of a woman in broadcasting who found herself suddenly unable to control her weight as she became more successful. All reasonable attempts at healthy diet and activity failed repeatedly, and the decline in her appearance began to interfere with that success (such is the business). Through therapy it came to light that years prior, during her communications schooling, she was informed by someone that she would "never get anywhere [in broadcasting] without sleeping with the right people." It was meant as a word of caution based on genuine concern and poor information, but stuck in her mind all the same. As she garnered attention for her efforts years later, her sub-conscious equated the impending success with the potential exploitation of her closely-guarded sexuality and formed a barrier to that negative expectation by lowering her appeal; all without conscious involvement or awareness.
Traumatic conditioning is much the same: a minor queue such as smell, the time of day or impressions of light and shadow, certain sounds, in addition to any overt similarities, can queue the sub-conscious to begin a protective response. Focus becomes selective once again and emotions and hormones run high, informing the conscious mind and primal instinct that fight or flight may be immediately necessary for self preservation. The similarity in physical and emotional reaction is so dramatically familiar as to force the recall of the original sensitizing event, bringing on the rehearsal of a deeply ingrained episode literally programmed into the mind.
Case in point, I recently had a minor weather-related accident in my car. The path of least destruction to others and property led me to a trajectory which damaged my driver's side C.V. axle and control arm, rendering the car undrivable and requiring extensive repair. I was not frightened or upset by the incident, though I did feel a little embarrassed for not judging the changing road conditions well enough and for the resulting financial setback. Once back behind the wheel, I found myself having moments of impending fear when decelerating for residential right turns: a startling, unbidden reflex out of sync with my (admittedly more cautious) thorough evaluation of the circumstances. It's taken me the better part of two months to unwire that reflex, and if not paying close enough attention or relaxing my efforts can still feel the sub-conscious intent.
No wonder then that severe, genuine trauma is capable of providing such long-lasting ill effects on the life and mental health of the sufferer. In an attempt to shelter a person from an anticipated real or imagined horror, it is possible for them to be adversely subjected to the same ill-affects they're trying to avoid. Due to the unintentional receptivity of the mind during the formation of the reflex, it's able to take root at surprising depth: easily enacted, difficult to remove. Common therapies attempting to soften the reaction through dissociative objective analysis (re-experiencing some elements in a safer environment, removing the reality of danger whilst maintaining triggers) can help, but may not ever be able to truly eradicate it. Could therapeutic hypnoanalytical techniques provide a better solution by addressing the triggers themselves?
I have not used hypnosis to remove my slight aversion to right turns, yet - I didn't think it disruptive enough to require such direct management. I also have not had opportunity to apply this to those suffering from any form of PTSD, though I'm intrigued by the potential. I'll have to give it a try on myself and report back.