To allow oneself to drop or fall with an easy, gliding motion; to slide down.

intransitive. To lower oneself in a slow, fluid manner into a recumbent, seated, or kneeling posture.

To sink to a low or lower level. intransitive. Of a person: to sink down into (also on to) a chair, etc.; to sink down on to the floor, etc. Also…

To glide, pass with an effortless motion; also, to descend gradually, to sink, subside.