Simon Usborne: Time seems to slow as you fall and then you hit – hard

They call it tombstoning not because it's a quick way to an early grave (although it can be) but because unless you enter the water completely upright, like a tombstone, you risk splitting open your swimming trunks or, worse, your skull.

It was a thought that caused my head to spin, my legs to quiver and my toes to tighten around the edge of the Pont du Diable (Devil's Bridge) over the Hérault river in the south of France. I was on holiday and the locals were hurling themselves off the 60ft (18m) stone structure. If they could do it... "I'm going to do that jump," I said.

Time slows when you make the final push into freefall. The ripples on the water seem to grow bigger as you descend and the fall is long enough that you have to circle your arms to stay upright. And then you hit. Hard. And if you don't tense your muscles you crumple like a demolished electricity pylon. I landed slightly off-vertical and jarred my back before staggering on to the bank, winded and bruised but elated and to cheers.

The next summer I met Connor and Sean, both 18, in Newquay, Cornwall. Their grandfathers had named the jumps here, working up to the 80ft cliffs on the edge of town. Before Connor disappeared off the Headland, a 70ft cliff above choppy seas, he told me it was safe. "It's the idiots who don't know what they're doing that get into trouble."

But Russell, a life-long jumper, once tried to backflip Headland while drunk. He hit the water sideways, broke a leg and was still on crutches a year later.