Using Fatigue over level drain

So my PCs are exploring a catacomb complex under an old temple having killed the orcs and goblins that were using the temple as a base.

This is their first ever dungeon and their first D&D campaign so as I stated in a previous thread somewhere I am being highly cliched in some of the aspects.

The temple catacombs were sealed to bind a demon. The tombs have not been opened for hundreds of years so the only creatures that exist are undead and demon and a couple of demon servants.

So with the undead I have been using fatigue as the touch effect. its been very successful I allow the PCs to cure a point of fatigue for a cure light (or 1 level of laying hands etc). If they are reduced to 0 fatigue by the creatures they will become undead.

It is successful because it
i) avoids the meta game level loss that makes no in game rational sense
ii) is much worse that HP damage as fatigue is long lasting (recover 1 point per long rest)
iii) its capped at 6 points no matter the level of the PC.
iv) fatigue has a death spiral with different ranks giving various penalties.

anyone else done similar

Using Fatigue over level drain