In other words, gains to your MHP should also go into your HHP.
Problem: I have 2 HHP left, luckily have Clovers, but unluckily can't find mouflon for shit. This is my forager/miner/main char, so I can't really do anything until I finish the mouflon hunting minigame, but it's just been dragging on and on... I'm sure I'll find one eventually when I can bring myself to try again, but it's just all very inconvenient. If I could use leeches, at least I'd have a semi-consistent way to grow out of my vulnerability, but at this point in time, I'd just die using them.
Solution: When Constitution goes up, you should gain as many HHP as you do MHP. From a logical point of view (this being an aside and not an argument for), becoming more conditioned should not simply raise the maximum amount of health you can achieve, but your actual current health. But of course, studying sticks won't teach you how to swim and etc., realism and all that not being important.
I tried to keep this simple, as for counter-arguments, I can't think of any. Of course, this probably wouldn't help someone with very high stats, as raising CON wouldn't be a simple task either, but those people also likely have access to sheep. I'd just like to throw this out there as a way to avoid predicaments like this in the future.