Looks like there is a defined (and unintuitive) order to healing afflictions.

There's some other stuff that seems to prevent units being healed but I don't know what that is about.

1. Battle fright, 50%
2. Feeblemind, 25%
3. Undocumented 137438953472, 50% heal rate, only healed if unit is not feebleminded as well
4. Disease, 50%
5. Crippled, 25%
6. Blind, 25%, only if unknown affliction 2147483648 not also suffered
7. One lost eye, 50%, only if affliction 2147483648 not also suffered
8. Weakness, 50%
9. Mute, 25%, only if unknown affliction 2147483648 not also suffered
10. Undocumented 2147483648, 20%
11. Undocumented 16, 25%
12. One lost arm, 25%
13. One lost eye, 50%, another chance
14. Chest wound, 50%
15. Limp, 50%
16. Never healing wound, 10%

2147483648 is likely lost head

137438953472 is likely dementia

1. Calculate (damage done*1000)/unit's max hp. Call this Value 1 and keep it for later.
2. Calc value 2: Multiply value 1 by the value of unknown unit effect 0x12d (I have no idea what this does). Then divide this by 100.
3. Final affliction value: Add 1 and 2 together
4. If cursed, add 150 to this sum
5. If active regen percentage is greater than 5, the value instead becomes (value * 100)/(regen percentage * 20)
6. Get affliction resistance. If liquid body is active, add 1 to this.
7. If (100/(affliction res + 1)) < random 0-99, set the value to 5.
8. If the final value is 5 or less, set it to 5.
9. First random roll: if the final value is not greater than a random number 0-999, do nothing. Otherwise, you get some kind of affliction (of which there are two different applying functions I don't yet know the difference between)

Practically, this means that regen reduces affliction chance to (500/regen %) percent.