Deathwalk

Your target must make a Wisdom saving throw or begin to suffer from extreme insomnia, which will lead into madness or even death. The creature will gain no benefits from long rests. For every full 72 hours that pass, the target will take 1 level of exhaustion.

Spells and other effects that induce unconsciousness for a period of 1 hour or more will reduce the creature’s exhaustion by one level but will not end the spell; likewise, spells that remove exhaustion will not be hindered but they will not prevent the creature from taking new levels of exhaustion.

After five days, and at the end of each day after that, the creature must make a Wisdom saving throw. On a failure, the creature suffers from short-term madness (Dungeon Master’s Guide, chapter 8: Running the Game), which will strike at some point during that day (the DM chooses when).

If the creature fails three saving throws (which do not need to be consecutive), it instead suffers from long-term madness; the creature will not need to attempt another saving throw until this madness ends. All failed saving throws after this point result in long-term madness. If, after beginning to suffer from long-term madness, the creature fails three more saving throws, then it will develop infinite madness. A remove curse or heal spell will end this effect.