MSFinals-5057

A 25-year-old male is brought into the emergency department on a Saturday night by his friends who suspect he has ‘taken something’. He appears anxious and cannot sit still, claiming that the walls appear to breathe and the floor is moving. Observations are not taken as he refuses, anxious that the nurse is plotting to hurt him. During the history, he intermittently will refer to himself in the third person and comment on his own actions as an observer. He has no past medical history and takes no regular medications.

What is the most likely cause of his symptoms?