if you were stabbed i'm pretty sure you would be laying down and not standing up, running a marathon
When others on the show have been stabbed they still move some. Look at Allison, she could move her hands and speak clearly and look around. Lydia wasn’t even breathing heavily, her head didn’t move, she could barely move her mouth, much like the Sheriff was doing just feet away. (Oh god, the sheriff and her mother?! WHY IS THAT A PLOT LINE?!)
Of course she’d be on the ground in pain, but there should have still been movement!