A PMHNP was assigned to a COVID-19 unit during the pandemic. Her assignment was to assist dying patients in saying goodbye to their loved ones via telephone. She facilitated their phone conversations and watched the patients have their last conversations with their family, often crying in agony. More than 2 months after this assignment, during which she assisted hundreds of patients who died, the PMHNP began having nightmares about these experiences. She had flashbacks of some of the memories, often triggered when she received a phone call or looked at her phone. She began avoiding using her phone. She began having difficulty with concentration and often couldn't remember details of her time on the COVID-19 unit. She often felt detached from reality and the world. What diagnosis is most appropriate?

Choice A reason: Major depressive disorder may involve sadness, anhedonia, and fatigue, but it does not fully explain recurrent nightmares, flashbacks, avoidance, and detachment after a trauma, making this diagnosis inappropriate here. Choice B reason: Generalized anxiety disorder is characterized by excessive, generalized worry and tension over multiple domains. It does not explain trauma-specific flashbacks or avoidance behaviors following a specific event, so it is not appropriate. Choice C reason: Acute stress disorder occurs within 3 days to 4 weeks after a traumatic event. Since the symptoms persisted beyond 2 months, the time frame exceeds that of acute stress disorder. Choice D reason: Posttraumatic stress disorder is characterized by intrusive memories, nightmares, flashbacks, avoidance, negative mood, and hyperarousal following trauma. The PMHNP's persistent and trauma-specific symptoms months after exposure are consistent with PTSD.