Medical emergencies at 40,000 feet

I was asleep, the plane dark as we flew over the Atlantic on our way from Johannesburg to São Paulo, when a familiar page came over the intercom: "Ladies and gentlemen, sorry to wake you. If there is a doctor on board, please hit your call button." This wasn't the only time my sleep had been disturbed for a sick passenger. The first time was on a flight from Chennai to Frankfurt. I was still a medical resident and, as I slid out of my seat to help, I realized that I had no idea what medications, equipment, or assistance, if any, I would find.