Are you heavier and taller while you sleep?

You can't gain mass while sleeping (except due to weight gain from eating just before sleeping) but you can get 'taller.' As you lie down, spine relaxes from lack of gravity's downward draw and when you wake you'll be a few milimeters taller.

I agree with WVHiFlyer. You cannot get heavier. In fact, you may get lighter because you are not eating or drinking but you are using up energy and releasing water in your breath and sweat. But you CAN stretch out.

Also, kids who are still growing can definitely get taller while sleeping--like a half inch in one night, I think I read somewhere.