I'd just roll with it, really. I'd hear them out and engage them in conversation -- perhaps starting with "could you get up off me please." Likewise with the police when they arrive... It wouldn't be my first suicidal encounter with them, so I know the drill. Obviously, this means an involuntary trip to the hospital, but again, I know it's at least sufferable, so whatever, I guess.
At least they care to intervene? The people I'd be upset with are the types who'd take out their phones, start filming me, and stand by while it happens for their entertainment. You know there's at least one in every crowd. If not 2 or 3 or 28 of them.