Seizure Disorder (Epilepsy): The patient's cell mate reports an unwitnessed seizure, which suggests a possible seizure disorder. This is the most likely diagnosis given the direct report of seizure-like activity.

Syncope: A fainting spell could be mistaken for a seizure, especially if the patient experienced a brief loss of consciousness and muscle tone.
Psychogenic Nonepileptic Seizures (PNES): These are episodes that resemble epileptic seizures but are not caused by abnormal brain electrical activity. They can be related to psychological or emotional distress.
** Substance-Induced Seizure**: Certain substances, including drugs and alcohol, can lower the seizure threshold and cause seizures in susceptible individuals.

Hypoglycemia: Low blood sugar can cause seizures, and it is crucial to rule out this potentially life-threatening condition.
Meningitis or Encephalitis: Infections of the brain and meninges can cause seizures and are medical emergencies.
Intracranial Hemorrhage: Bleeding within the brain can cause seizures and requires immediate medical attention.
Traumatic Brain Injury: A head injury could have caused the seizure, and it's essential to assess for any signs of trauma.

Hashimoto's Encephalopathy: A rare condition associated with autoimmune thyroiditis that can cause seizures among other neurological symptoms.
Vasculitis: Inflammation of the blood vessels in the brain can lead to seizures, though this is a rare cause.
Parasitic Infections (e.g., Neurocysticercosis): Certain parasitic infections can cause seizures, especially in individuals from or traveling to endemic areas.