So, contrary to increasing the fun, death spiral mechanics often decrease the fun for most players.
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I think that is going to highly depend upon the player. You did somewhat mention that in your post (the one I'm quoting,) but I wanted to point it out again. There are many people (myself included) who enjoy having damage actually mean something. I'd say such systems decrease fun for some players, but I wouldn't necessarily say "most" players.
That being said, I do very much agree that it wouldn't make a lot of sense to implement such a system into D&D. I feel that way because D&D is built in such a way that -I feel- treating HP strictly as physical damage doesn't mesh very well with the rest of the system. Likewise, it doesn't mesh well with some of the other assumptions and abstractions that D&D tends to make. Instead of trying to force such a system into D&D, it makes more sense to me to play a different game if you want a different game.
Personally; as I've already said, I enjoy having damage mean something to a character's ability to fight. There are many reasons why, but one which comes to mind for me often is that (imo) it adds consequence to combat. A byproduct of those increase consequences are that other avenues of problem solving become more viable. I love combat as much as the next person, and I do enjoy battle scenes in games, but sometimes it's nice to know that whacking away at a bag of HP & XP isn't always the right answer to every problem. It's also nice -as a player- to feel as though the points you put into learning a new language or the points spent to learn a skill weren't wasted because the game assumes you'll just kill everything.
I also find that such a system does add a dramatic element. The heroes winning at the end of the day despite being beaten and broken is a staple in many stories. While there are also stories in which the hero seems barely phased by anything and defeats the enemy simply due to having more ability to absorb damage, I personally find them less interesting. That's not to say I don't sometimes enjoy playing impervious characters; at times I have, but it's nice to have other choices as well. It's also nice to be able to look at combat as combat and injury as injury rather than a strict equation of numbers. I remember a D&D encounter I had once in which I was taking damage, but the enemy was taking more; without any changes being made to our fighting ability, it was obvious I would outlast the enemy.
Having tactics and strategy matter is a nice side effect I've noticed in games where combat is giving a bit more grit and detail too. Fighting as a unit and as a team is something which tends to be encouraged when you can't just hack through everything solo with no fear because you either a) have enough HP to outlast everything or b) facing doesn't matter, so it doesn't matter if you get surrounded. Do I think it's cool and heroic to charge into the enemy guns-a-blazing? Yes, I most certainly do. However, I also feel that fighting smart should product results which are generally consistent. I want cool stunts and moves to be available, but it's nice to know that tactic decisions can also matter. ...I started branch off into talking about facing and some other things there, but those things do also tie into HP being less abstract; you can mitigate the idea of a "death spiral" being a certain thing by working as a group. In games which are generally meant to be played with multiple players, I see that as a good thing.
I've recently started reading HackMaster Basic. There are what I feel some excellently worded bits of advice provided in it. I think they are relevant to what I am saying here, but I don't want to quote someone's product without permission. It's a fee product, so readily available to anyone interested in seeing something which has a different mindset behind it than the modern versions of D&D.
http://www.kenzerco.com/hackmaster/
To answer the OP, I can only echo what many others have said. There are games which have something similar to what you are suggesting. For example, the other game I primarily play (other than D&D) is GURPS 4th Edition. In GURPS, your ability to fight can be hindered by damage and injury. GURPS also has both HP (hit points) and FP (fatigue points.) One measures your body's ability to take damage; the other measures fatigue. You can spend fatigue to put some extra oomph into an attack; make a feverish last ditch effort to defend against something; keep running during a long chase, and many other things. The default magic system also uses FP as a way to power spells -something which makes sense to me since nearly every game (including D&D,) novel, and movie I'm familiar with tends to emphasize how difficult and tiring it is to master magic.
It's important to also note that GURPS also has active defenses. While taking damage has a much more physical element to it than losing HP in D&D does, the game (GURPS) also does not assume you will get hit in the same way that D&D does. You can try to dodge out of the way; parry with a weapon, and/or block with a shield. You don't get hit simply because the other person rolled better than your AC. I believe this difference is important because I also believe that a system which had a "death spiral" in combination with abstract defenses would tend to lead to the lesser amount of fun mentioned in the post I quoted. I believe that because I feel (from a player's perspective) it wouldn't be fun to have my ability to fight hindered by damage without having an active way to avoid that. Though, that is a personal view; I would never suggest my view is the right one or the most common one. Much like HackMaster Basic, GURPS Lite is also free and allows you to see the basics behind how the game works.
http://www.sjgames.com/gurps/lite/