To allow one's shoulders and head to slump, droop, or hunch forward or to one side. You need to stop slouching over like that while you work at the computer, or you'll give yourself major back pain down the line! Everyone in the meeting had started to slouch over, their eyes glossing over out of sheer boredom.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
to lean or crumple and fall to one side; [for someone] to collapse in a sitting position. He slouched over and went to sleep in his chair. When he slouched over, I thought something was wrong.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.