General:
* Lean
* Stoop
* Hunch
* Bow
* Curve
* Incline
More specific:
* Slouch: (Suggests a relaxed, ungraceful bending forward)
* Crouch: (Lowering the body close to the ground)
* Duck: (Bending forward to avoid something)
* Sag: (To sink or droop downward, often due to weight)
Formal:
* Flex
* Incumbent: (To be lying down or resting)
The best word to use will depend on the specific situation and the intended meaning.