I have a thorn in my side. Not metaphorically, you understand: I literally have a thorn lodged in my side.
It's been there about 14 years. It's in my back really, but just at the point where my back starts to curve around, so I can legitimately call it my side.
How can it have been sitting there under my skin for all that time? Well, it entered with a lot of force: all the force my body had acquired in falling for about six feet.
What happened was this: I was exiting the block of flats I lived in in my first year of university, which entailed descending a set of steps. The steps had a wall or barrier at about waist height, and without any consideration, without any thought of how high the steps were or what might lie on the other side, I vaulted the wall - surprising myself as much as my two friends - and a short while later landed feet-, hands-, arse- and back-first in a thorn bush or two, with about a dozen punctures as a consequence. The thorn in my side went unnoticed at first, and then resisted persistent efforts to squeeze it out.
I wouldn't be writing about this if the incident had been a one-off, a youthful quirk or spasm never repeated. On the contrary, that occasion marked the first instance (as far as I can recall) of something I've since become intimately acquainted with: the near-irresistible compulsion to vault waist-high barriers between myself and a drop or otherwise dangerous location.
I don't know if there's a name for this specific urge. Google informs me that there is a name - the high place phenomenon - for the urge to jump from high points, but I don't get this feeling with heights in general: drops without barriers or with say 6-foot glass windows cause no such urges. It's only waist-high barriers, on bridges, steep slopes, buildings, metro platforms, etc, that bring it powerfully forth. Maybe I was a hurdler in a former life.
Hungerford bridge in London, which joins the popular South Bank cultural area with its more hinterlandish partner on the other side of the Thames, is one of my favourite spots because of its views of buildings like the Gherkin in The City, but I often have to avoid the edges or take firm hold of my consciousness when I'm crossing it because of what I might do otherwise.
The thorn incident is the only occasion I've actually succumbed to this urge, but if I ever do again it'll probably mark the last time I ever feel any urges of any sort, given the likely outcome.