A 29 Year Old Male Fainted Outside A Store, Hitting

A 29 year old male fainted outside a store, hitting the back of his head on the pavement. Not sure how long he was unconcious. Complained of blurred vision - described it as "broken rainbow prism". Was nauseous, but did not vomit. Some dizziness, unsteadiness. He feels chilled (body feels cool). Very drowsy, can't keep his eyes open, is now sleeping. He doesn't want to go to an ER... but I'm concerned. Do I let him sleep? Do I wake him periodically and just watch him?