You are seeing a 21-year-old male in A&E who has presented with an episode of loss of consciousness. During the history the patient informed you that prior to his loss of consciousness he felt a strange rising sensation in the abdomen. His friend who attended with him informed you that this loss of consciousness lasted 3 minutes and was characterised by generalised stiffening and subsequent rhythmic jerking movements of the limbs and tongue biting. What is the most likely diagnosis?