Да и вам не спится?
What that means is, "And you too are just lying there, wide awake, not feeling sleepy/drowsy, having difficulty falling asleep?" That person regards such a feeling a necessary stage of falling asleep, so the answer "Мне никогда не спится" is surprising for him (as it would be for me, or anybody else -- it's a phrase you are unlikely to hear, ever, and as such it sounds like a joke) and he asks "Как же так?", to which another person replies that one moment he is wide awake and then he switches off, just like that.