Quick answer: Drink it off. Wine removes 25–35 insanity, chocolate 20, a tavern beer 12; early on a berry pie removes 3. Sleep only clears insanity (−20) when you had the Lack of Sleep debuff — a normal night does not touch it, which is why the purple bar "isn't going down". Writing stories at the desk also lowers it by 1 per tick.

This page covers insanity, insanity not going down and как сбросить безумие.

Why sleep didn't fix it

In the 100% run: "if I didn't have the tired debuff, my sleeping didn't remove insanity." Sleep removes 20 insanity only when you are sleeping off Lack of Sleep.

What raises insanity

  • Digging, burying and exhuming graves
  • Autopsies
  • Making headstones, fences, graveyard signs and zombie collars
  • Collecting honey
  • Some food: Soldier's ale +20, Baked meat +10, Flesh +10, Burger +5, Sandwich +5
  • Spending energy while you have Lack of Sleep (+0.5 per point)

Insanity caps at 80, which leaves you only 20 energy — see Energy.

What lowers it

Item / actionInsanity
Wine (gold / silver / bronze)−35 / −30 / −25
Chocolate−20
Sleeping off Lack of Sleep−20
Beer (buy at the tavern)−12
Berry pie−3
Writing stories at the desk−1 per tick

Related

Sources: a 7-tips guide and a recorded 100% playthrough on YouTube, wikily.gg.