Q:

Is this houserule about hit points balanced?

As a D&D5e DM, I always feel that HP in D&D are somehow unrealistic. Either it's "there is no difference between 1 HP and 100% of my HP" or "I took too much damage in one hit, so I'm dead".
So I tried to make a houserule somehow inspired by the Vampire: the Masquerade HP system.
Here's what I ended up with:

Each time your character takes damages that reduce them below 50% or less of it's current HP (on one hit), it takes a penalty, which becomes stronger each time it occur (reset on long rest)
e.g. you have 100 current HP. You take 50 (or more) HP of damage on one hit. Your character get a penalty. Now it current HP are 50. So, if it is not healed, it will get another one if it takes 25 (or more) HP of damage.
First time you have disadvantage on your rolls until your HP are restored to 100% (or you are taking a long rest).
Second time something broke in you (your arm, your leg, etc.), which will give you disadvantage on rolls using this limb.
Third time you take a permanent wound (a.k.a. you have this disadvantage until you got a regeneration spell or equivalent).
Fourth time you are dead.

Is this houserule balanced? If not, what could I do to improve it?

Balanced compared to what?"
I mean balanced compared to the actual system, or compared to the alternatives (DMG, Unearthed Arcana)
Implementation issues already considered:
How difficult is it for me to keep track of enemies and their HP reductions?    Since I use Roll20 as a support, it is not that hard. (so I can guess that most of combat tracking app could do the job)
I checked out the DMG & Unearthed Arcana's optional HP rules.  I don't like those rules as they are, even if I used them as a source of inspiration.
I polled my players about this, and those who helped me test a basic version of it really like it.

A:

So we’re looking at the following health systems in question:

Standard, aka critical existence failure
Vitality/Wounds
Lingering injuries
Your homebrew, which I’ll call ‘injury levels’ here (after the exhaustion mechanic it resembles).

Injury levels vs standard is barely a comparison; the PCs are being directly downgraded with nothing to show for it. Their only saving grace is if this applies to their enemies too, but this fundamentally changes combat in your game; we’ll come back to that.
Comparing injury levels to lingering injuries, it’s going to be easier to inflict penalties. Any hit that leaves a lingering injury (ie a crit) is likely to inflict an injury level as well, but as your target (or you) get lower in health, injury levels will only require half the damage to inflict, while crits remain unpredictable and get no more likely.
Vitality/Wounds though, is an interesting comparison. It’s possible that bumping the consequence of a crit from a lingering injury to outright ignoring most of your resilience could balance it against your injury levels, but they’re going to have slightly different effects on combat deadliness - reliably inflicting injury levels makes it hugely more dangerous but only to the losers, while instakill crit-to-wounds makes it dangerous to EVERYONE, even to the winners.
The main effect of adding a ‘death spiral’ mechanic is going to be that going first becomes much, much more powerful, which will make Dexterity even more so the One Stat To Rule Them All and make every battle resemble a single stroke ninja duel. Expect to see first hit become the only strategy, if it’s this capable of literally annihilating the target’s capability to execute any strategy at all.
The only problem with all of this is that 5e monsters are built to different designs than the players, in ways that might stymie the “it works on everyone” part of these systems. That will take playesting.

