This is a funny topic. I've had some lady fall asleep next to me on a bench. She started to lean towards me so I got up quickly and she hit the bench with her head. It was a little funny and sad at the same time
It's happened to me usually on airplanes, and a crowed subway at am rush hour.. but a polite nudge wakes them up. No need to run like they have the plague or something.. there is a lot worse that can happen to you than having a total stranger nod off in your direction..