disease of the heart
癊 refers specifically to a disease of the heart, a medical condition affecting that organ.
癊 combines the sickness radical 疒 with 陰, which likely provides the sound イン and may relate to the heart condition through its meaning of 'shade' or 'hidden', but the exact historical development is uncertain.
The sickness enclosure 疒 wraps around 陰 (shade, hidden). Imagine a hidden, shadowy ailment deep within the heart—a disease that lurks unseen.
For イン, picture an inn where a guest is secretly suffering from a heart disease: inn -> イン, and the sickness is hidden inside like the 陰 component.
—