The container feels ... small even though it isn't. Shrinking ... compounds injuries. His clothes don't shrink with him, instead he's just a tiny thing, finding limbs difficult to move. He tries making himself smaller, knowing he's trapped, trying not to panic, trying not to ... let her notice.
But of course she will. She can see him. He shouldn't have drunk it. Of course... the worst thing is - he's not sure what's worse. The fact that he could probably fit in John's giant paws or that he might never see John again. He presses his hands to his face, trying to burn the image of John's smile on the tarmac in his small, tiny brain.

Small. Tiny.
You're such a stupid little boy, Mycroft sneers at him. And Mummy and Daddy are very cross...