This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
癁 combines 疒 (sickness) with 復, which likely contributes the sound. The exact historical development is uncertain.
The sickness enclosure 疒 wraps around 復, suggesting a recurring illness. Without a clear meaning, picture a sickness that returns again and again.
For フク, imagine a recurring sickness that makes you feel like you're stuck in a loop: fuku -> フク, like a bad luck cycle.