As a child playing crazy golf - swung the club back nice and hard into the back of my own head.
At college got knocked off a chair by an Akro scaffolding pole that I hadn't secured and it hit my head. I must have a hard head as I was just a bit stunned.
Staggered downstairs at 6am to make a cup of tea and slipped off one turning stair - my ankle made a horrific noise and I wasn't sure if I was going to be sick or pass out. I tried shouting for DP but he was oblivious so ended up having to crawl up the stairs and dragged myself over the ottoman at the end of the bed to grab his foot as he was still snoring. He shot up in bed and screamed - I had long black hair at the time and he woke up to what looked like the woman out of the Ring clawing at his foot and whimpering.
As it was early and we didn't fancy a trip to A&E at such an ungodly hour, I necked two Ibuprofen with a half finished glass of rose I had by the bed, he got me a bag of frozen peas and we crashed out again, hoping it was just a sprain.
When we woke up again, my right ankle had swollen to such alarming proportions I had to go down the stairs on my backside for the inevitable hospital trip.
After being scolded for taking two Ibuprofen instead of one, had to have my foot manipulated several times because the x-ray wasn't quite right three times, and finally been told it was "just" a stable fracture requiring a boot, the doctor backed me out of the tiny consulting room we were in, swung me round in the wheelchair with my right foot on the outstretched bit right into a metal bin. Love the NHS, but bloody hell.
Also in the 90s, was being starved for surgery in hospital that kept being put back to accommodate emergencies - fair enough. Pre mobile days of course, so my Mum rang the ward to see how it was going. Went to the nurses desk, managed to say "hello" and the next thing I know I'm being brought round on the floor as I'd passed out and gone down hard. Funnily enough the surgery happened pretty quickly after that, but I went home with a stonking black eye.