A 26-year-old female is brought to the emergency department by her family 10 days after the sudden death of her mother in a car accident. She has no prior psychiatric history. Over the past 5 days, she has developed the belief that her mother is communicating with her through the television, she hears her mother's voice giving her instructions, and she has been observed talking to someone who is not present. Her speech is disorganized at times, and her affect is labile. Her family states that prior to her mother's death she was functioning well, working full-time, and had no behavioral concerns. Urine drug screen is negative, and medical workup including CBC, CMP, TSH, and urinalysis are within normal limits. The symptoms began abruptly 5 days ago. What is the MOST likely diagnosis?