You can often guess the meaning of new words through context, as in this case. Slouching or sprawling describe positions of poor posture. Sprawling would pertain to sitting, slouching to sitting or standing, a failure to be erect.

1.If you slouch, you sit and walk in a lazy or tired way with you head and shoulders drooping down. EX. Dude, you are certainly no slouch at the kiten! 2.If you sprawl or sprawl out somewhere, you sit or lie down and arms out in a careless manner; A place sprawls covers a large area, with various parts extending untidily in different directions. EX. I tried to pick it up, but i overbalanced in the process and fell sprawling.