Most serious trouble I've been in? Well - this wasn't with a human being, this was with the elements.
'I know, I'll climb the highest mountain in England, setting off at 5pm, with no provisions, no phone, no map, no compass, very casual clothing (nothing rainproof) not telling anyone where I'm going, in cold late October. Yay what a plan'.
My fitness got me to the top, at about 9pm, and it's getting dark. Then I got (100% completely) lost, freezing cold, and the exact opposite of hilarity ensued.
I could have, quite literally, got myself killed from exposure. It was totally pitch black, freezing, massive windchill, oh, and no-one to inform mountain rescue of the problem.