sink back
sink back into something

Markham sat up suddenly, then sank back with a shrug.

He tried to sit up, then sank back with a moan.

Sinking back with a groan, he decided to put off his next attempt indefinitely.

She sank back a little and hugged the pillow tighter.

Grace sank back with a sigh into her chair.

He sank back a bit in his chair and stared at the tabletop, seeing something quite else.

Dazed by her tumble, the girl sank back with a sigh.

She heard him reach for it and sink back with a sigh into the deep armchair.

She sank back with a little shiver and her large brown eyes seemed to droop.

Lord Charles sank back with a look of half- comical despair.