illness, sickness, disease, pain
疴 centers on physical suffering: illness, sickness, disease, and the pain that comes with them.
疴 combines the sickness radical 疒 with 可, which likely contributes a phonetic element. The exact historical development is uncertain.
The sickness enclosure 疒 wraps around 可, like an illness that is 'possible' to overcome. Picture a person inside a hospital room (疒) nodding 'yes, I can' (可) despite the pain.
For ア, imagine the sick person letting out a weak 'ahh' sound of pain: 'ahh' -> ア, and the illness makes them groan.