A 20-year-old man suffered a significant closed head injury after a diving accident. He is left with minor memory impairment but makes a full recovery. A few months later, he has a witnessed loss of consciousness with some arm and leg twitching. After the event, he is disoriented for 2 hours and then gradually returns to baseline. There was no incontinence or tongue biting, and his examination is normal. Which of the following is the most likely diagnosis?

This man had a generalized posttraumatic seizure. The prolonged confusion after the event suggests seizure rather than syncope. In the majority of cases, seizures do not develop until several months after the injury, 6-18 months being the most common interval. The more severe the injury, the greater the likelihood of seizures. For severe injuries, some authorities recommend prophylactic anticonvulsants for 1-2 years. There is no firm evidence for this, however.