A 32-year-old man is brought to the ED by his partner after several hours of increasing agitation and confusion. Earlier in the evening he had complained of feeling unusually hot and flushed. On arrival he is disorientated, speaking incoherently, and repeatedly trying to get off the trolley.

His skin is warm and dry and his pupils are noticeably enlarged. He has a fast, regular pulse. He is unable to pass urine despite feeling “full,” and nursing staff note absent axillary sweating. Shortly after arrival he has a brief generalised tonic–clonic seizure.

Temperature is 38.6°C. Blood glucose is normal.

What is the most likely diagnosis?