bed
蓐 centers on a bed or sleeping mat, often made of straw or grass.
蓐 combines 艹 (grass) with 辱, which likely contributes the sound. The grass radical suggests a straw mat or bedding.
Grass 艹 over 辱: imagine a thick layer of grass or straw spread out as a simple bed.
For ジョク, picture a joke about a lumpy grass bed: joke -> ジョク, and you laugh at the uncomfortable straw mattress.
sickbed