This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
疜 combines the sickness radical 疒 with 下, but the exact historical development and original meaning are uncertain.
The sickness enclosure 疒 around 下 (below/down) suggests something going down or out, but the meaning is unclear.
For カ, imagine a car (カ) driving down (下) while sick (疒): car -> カ, and the sickness makes it go down.