He took in a sharp breath as Jim jerked him forward, right before spilling (completely undignified--!) into his lap. His automatic reaction was to twist and squirm, try to loosen the grip Jim had on his clothing and then--

Spock froze, turned his head to look up at Jim with wide eyes, and then reached up for his throat. So what if maybe the sudden weight distribution (and the continued twisting/squirming) would likely pull them both out of the chair?