Problems sleeping are common after exposure to highly threatening experiences and can occur with and without a diagnosis of posttraumatic stress disorder (PTSD). Established treatments for PTSD are limited for addressing insomnia and many insomnia treatments appear to be limited in the context of PTSD. Suvorexant is FDA approved for insomnia and among approved drugs has a unique mechanism of action that may be well suited for targetting arousal at night dysregulated by trauma. The investigators will evaluate the efficacy of suvorexant for insomnia that developed in relation to trauma exposure, utilizing a placebo control, and polysomnography to identify biomarkers of response, in a six week trial.