weakness, infirmity, retention of urine
癃 centers on a state of physical depletion: general weakness, infirmity, or the specific inability to pass urine. The meanings share the idea of bodily function being obstructed or drained.
癃 combines 疒 (sickness) with 隆, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to illness.
The sickness enclosure 疒 surrounds 隆, which can suggest something rising or swelling. Imagine a body so weak that even normal functions become obstructed, like a blocked passage.
For リュウ, picture a weak person trying to hold onto a single 'ryu' (as in 'dragon') charm for strength, but the charm slips away: ryu -> リュウ.