In fact, the specific causes of sleep disturbance in posttraumatic stress disorder (PTSD) sufferers, the most prominent of which are insomnia and nightmares, have not been determined. However, sleep impairment is the most often reported of the 17 PTSD symptoms and is considered one of the most refractory to treatment. It is theorized that PTSD sleep impairment relates to the hypervigilance inherent in PTSD such that sleep is disrupted by the perception that vigilance (in response to perceived threat) must be maintained at night. Sleep impairment seen in PTSD sufferers may then result from increased physiological arousal associated with chronic hypervigilance. Hypnosis provides deep relaxation which is hypothesized to decrease overall hyperarousal. Nightmares and trauma cues can further disrupt sleep through learning and conditioning. PTSD sufferers may learn to associate nighttime cues with danger and conditioned emotional responses to these cues may disrupt sleep. Detecting relatively innocuous environmental stimuli (i.e. normal nighttime noises) while trying to fall asleep and interpreting them as dangerous increases arousal. Hyperarousal interferes with sleep and has been identified as causal in the development of non-PTSD insomnia. Beyond decreases in general hyperarousal, an additive benefit of the hypnotic trance and the use of post-hypnotic suggestion would be the facilitation of new learning such that bedroom stimuli could become associated with pleasant, restful images. The use of hypnosis as a complement to CPT, an empirically supported, cognitive-behavioral intervention developed to treat PTSD, could specifically remediate 1.) sleep onset and maintenance deficits, 2) the frequency and intensity of parasomnia episodes, and 3.) cumulative sleep deprivation. Acquisition of the skill of self-hypnosis will provide PTSD sufferers with a tool to regain normal and restorative sleep patterns. Restoring sleep will enhance the efficacy of CPT in remediating psychiatric symptoms (PTSD and major depression), reduce overall physiological reactivity, increase psychosocial functioning, and decrease somatization.