I found this too death spiral-ey since 5e just has Exhaustion, rather than Fatigue & Strife (two tracks means it's less dire but still hampering).Best incremental rule to add:
- A character takes a level of exhaustion when dropped to 0 hp
...also, I like the prestige check a lot, and different types of initiative rolls!
For my 5e games I houseruled DC15 Con when reduced to zero hitpoints to avoid a level of exhaustion. IMO it's a good middle-ground. It's easier for martials and tough characters, and it's always good for martials to get another tick in their favor in their losing battle vs caster balance.
Now I think about it, maybe DC 1/2 damage that dropped you to (min DC10) would be a better long-term rule.
Or maybe using a5e's instant death/megadamage rules?