First, ask the cabin crew to stay with you for any assistance that you might require. Then proceed to assess the patient as you would normally do elsewhere. As the great majority of these incidents are benign, the result of vaso-vagal syncope, by the time you have confirmed that the passenger has a good pulse and is breathing normally, the passenger will likely have regained consciousness. A few more minutes in a supine position and the passenger will be ready to return to his seat without further problem.