The Hypothermia Fic is particularly common in the LOTR fandom, presumably because large numbers of readers and viewers have worked out that since the action of the trilogy takes place between late September and late March, in somewhere having approximately the latitude of England, and the characters (particularly in the film) keep falling into rivers in their only set of clothing that there is a lot less hypothermia around in the text than they deserve. In fact, in TTT I couldn't understand why Aragorn who manages to fall into a river fully clothed when concussed and Sam who dives into another river fully clothed while wholly unable to swim, in each case it what must be at least mid-November, don't suffer more as a result. I know Aragorn gets the benefit of the SAR horse, but even so (yes, I know Tolkien didn't write the SAR horse, but he wrote the pony with inbuilt GPS and homing radar, so he can't talk).
The problem with the hypothermia fic is that real people with hypothermia are jolly cold (and, in the LOTR scenario, usually pretty soggy, too). Meaning that cuddling them, although medically recommended (thus getting neatly over the innocent explanation bit) is rather like clutching at a cold clammy thing that is either unconscious or making incoherent noises. Recovery is signalled by the onset of violent shivers. If you find this erotic, you probably also like squid porn (I'm doing cliches here, so I will omit reference to the Snape/squid fic which began with him initially attempting to handle his cephalopod fetish by surreptitious visits to the local fishmonger).
This shades, actually, into the other way teenage werewolves get to have sex, which is if one of their schoolfriends happens to think it's the only way to distract them from committing suicide. Apparently werewolves always attempt suicide by launching themselves off tall buildings. I can see, logically, why in the circumstances shooting oneself would be right out, but I do wonder why doing a quiet bit of stoppering death never occurs to them as a way of shuffling off this mortal coil? Or, if muggle-born, the old exhaust-pipe and hose trick?