Wow, amazing, Eva.
Mine is probably when I was in high school -- I'd stopped menstruating, and was put on some drug to start it again. (Nevermind what I actually needed was to eat more and exercise less...) I was at school when I got some absolutely horrible cramps. Went to the nurse's office, got permission to go home. Evidently looked awful. My dad (who I lived with at the time) was at work and unreachable, I planned to take the city bus home. Involved walking a block or two, not bad.
I set off across a field towards the bus stop. Up 'til that point, it was bad, but then it kicked into something surreally awful. I clutched my tummy and collapsed on the field. I couldn't shout, it was like it didn't even occur to me, I was so focused on the pain. I lay there in the fetal position for a long time, expecting someone would show up soon... nothing.
Anyway, went on in that vein for a while -- agony, collapse, expect help, nothing, get up, agony, collapse -- and somehow (it's a blur) I made it home. (Dunno why I kept trying to get home rather than turning around and going back to the nurse's office -- wasn't thinking very rationally.)
Lay there in the worst pain I've ever experienced -- far worse than childbirth -- on the couch, unable to move, waiting for my dad to come home, when my mom burst in the door.
They had been divorced for a few years at that point, she never came over. She was a homecare nurse, would drive around visiting patients at their homes, and was driving on a major street one block away when she got an urgent page -- my dad's house was the nearest phone. (No cell phones then.) She barely registered me, rushed to the phone, called... but nobody had paged her.
Then she saw me.