Losing 5 or more Sanity in one go risks a temporary break; running Sanity too low risks a longer-lasting one.

Summary

Losing 5 or more Sanity in one go risks a temporary break; running Sanity too low risks a longer-lasting one.

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If a single Sanity loss is large enough (typically 5 or more points in one roll), the investigator risks a bout of temporary insanity — a Keeper- or player-chosen reaction (catatonia, a phobia, a violent outburst) lasting for a scene or so. If an investigator's Sanity drops to a fraction of their starting maximum (commonly one-fifth), they risk indefinite insanity — a longer-term breakdown that persists across sessions until treated. Neither state is meant to sideline a player permanently; both are opportunities for the character to come back changed.