へたり込こむ

godan verb (-mu)

collapse into a sitting position; sink down to the floor

Describes slumping down heavily, often from exhaustion, shock, or weakness. The movement is sudden and uncontrolled, ending in a seated or crumpled posture.

• 疲つかれ果はてて、玄げん関かんでへたり込こんでしまった。

  Exhausted, I collapsed into a sitting position at the entrance.

• ショックのあまり、彼かの女じょはその場ばにへたり込こんだ。

  Overcome with shock, she sank down to the floor right there.