DS1 slid down the stairs (steep ones too, that can't have a stair-gate), head first on his stomach when he was around 16 months (lay on the landing peering over the edge when I turned my back to close a door and I turned round to see him punt himself over the edge like he was on a skeleton bob).
He rolled over and round as he went and I'll never forget the sight as I ran down after him praying his head would miss the brick pillar at the bottom (it did).
I gathered him up as he sobbed, ran back upstairs with him, cuddled him and then placed him lovingly on the bed as I straightened his cot bedding to pop him in there while I tried to stop shaking and decided if we needed an ambulance.
Turned round at a scream to find him falling backwards off the bed (which he'd previously done for the first time at 10 months) and hitting his head on a wardrobe shelf on the way down.
Really not my finest morning as a mother
. He was fine - just shocked after both incidents rather than injured. After cuddles and when I'd convinced myself there actually wasn't a mark on him, he had a lovely doze while I drank tea, sobbed and phoned DH at work to try and calm myself down 
Plenty of bumps and bruises since - he'll be 2 next month and doesn't seem any the worse for it.
DS2 is three months so it's only a matter of time before it starts again! DS1 hasn't already sat on DS2 accidentally...twice...oh no, that hasn't happened at all....