illness, pain, neglect, useless
瘝 centers on a state of being afflicted or diminished: illness and pain as direct suffering, and neglect or uselessness as the resulting inability to function.
瘝 combines the sickness radical 疒 with 眔, which likely contributes a phonetic element. The exact historical development is uncertain, and the character is rare.
The sickness enclosure 疒 wraps around 眔, which looks like an eye 罒 over a tangled mess. Picture an illness that clouds your vision and leaves you feeling useless and neglected.
For カン, imagine a can of medicine that has been neglected and is now useless: can -> カン, and the sickness inside 瘝 remains uncured.