It's an obvious transition - nosebleed aside, there is nothing similar about Sam's expression when Sylar drops. There is no thought of pain or shock, just a white face, panicked because he is dangling over a parking lot and does not want to be dropped.

That he's far too exhausted to pull himself up isn't helping.

Still, his fingers twist to grab onto Dean's wrist and he gasps, strained "Help-"