A 25-year-old man presents to the Emergency Department following a generalised tonic-clonic seizure lasting approximately 3 minutes, which resolved spontaneously. He has no prior history of seizures and no obvious precipitating factors. He is now post-ictal but recovering well, GCS 14 (E4 V4 M6), with normal vital signs and neurological examination. According to NICE CG137, what is the most appropriate immediate management plan?