This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
瘇 combines the sickness radical 疒 with 重, but the exact historical development and original meaning are uncertain.
The sickness enclosure 疒 surrounds 重 (heavy), suggesting a heavy illness or swelling, but the exact meaning is unclear.
For ショウ, imagine a heavy sickness that makes you shout in pain: shout -> ショウ, tied to the heavy feeling inside 瘇.