sagging

(verb) droop, sink, or settle from or as if from pressure or loss of tautness. Synonyms: sag, droop, swag, flag.

(verb) cause to sag. Synonyms: sag, sag down. Example: "The children sagged their bottoms down even more comfortably."

(adj) hanging down (as from exhaustion or weakness). Synonyms: drooping, droopy.