Full Idea
Health is natural for the healthy but unnatural for the sick, and sickness is unnatural for the healthy but natural for the sick, so we must give credence to the natural perceptions of the sick.
Gist of Idea
Sickness is perfectly natural to the sick, so their natural perceptions should carry some weight
Source
Sextus Empiricus (Outlines of Pyrrhonism [c.180], I.103)
Book Reference
Sextus Empiricus: 'Outlines of Pyrrhonism', ed/tr. Bury,R.G. [Prometheus 1990], p.46