This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
瘒 combines the sickness radical 疒 with 軍, but the exact historical development and original meaning are uncertain.
The sickness enclosure 疒 around 軍 suggests an illness related to military or group activity, but the exact meaning is unclear.
For ゴン, imagine a gone soldier inside the sickness enclosure: gone -> ゴン, and the soldier is ill.