The following rule adapts the idea of Stress as a game mechanic, similar to the rules found in Unknown Armies, Mothership, or Liminal Horror. In most cases, a character should be allowed a Wisdom saving throw to avoid gaining a level of Stress. The DC depends on the severity of the cause (DC 10 for experiencing ordinary violence, DC 15 for seeing a dead body, DC 20 for seeing an eldritch horror for the first time). Heroic characters may get advantage on this saving throw.
Stress [Condition]
While you have the Stress condition, you experience the following effects.
Stress Levels. This condition is cumulative. Each time you receive it, you gain 1 Stress level. You panic if your Stress level is 6.
D20 Tests Affected. When you make a D20 saving throw against either the Stress or Frightened conditions, the roll is reduced by 2 times your Stress level.
Mental Vulnerability. Each time you suffer psychic damage, increase the damage by your Stress level.
Removing Exhaustion Levels. Finishing a Long Rest removes 1 of your Stress levels. When your Stress level reaches 0, the condition ends.
PANIC TABLE (like insanity)
Roll on this table when a character reaches Stress 6.
Roll 1d6
* 1 … Faint. You become unconscious for 1d6 rounds, or until another character uses an Action to awaken you.
* 2 … Freeze. You are struck by momentary catatonia. You are paralyzed until the end of your next turn, then suffer the Frightened condition for 1d6 rounds.
* 3 … Fight. You won’t go down easily. You must spend your next action attacking the source of your panic. Casting a damage-causing spell is also allowed.
* 4 … Flight. You must get away. You are Frightened by the source of your panic for 1d6 rounds.
* 5 … Fawn. If you just do what it wants, you’ll survive. You are Charmed by the source of your panic for 1d6 rounds.
* 6 … Frenzy. An adrenaline surge increases your movement rate by +5 feet, you gain advantage on melee attacks, and have advantage on all saving throws for 1d6 rounds.