Hiya, don't know about the numb bellybutton but I can so relate to the floppy feeling, I've had that a couple of times when I've been particularly active, almost as if I've used too much energy at once?!?!? I've also noticed that if I haven't kept on top of my water intake, I feel quite weak and limp, so try and make sure I've had 2 litres by lunch and another 2 by evening.
Hope your bellybutton resumes feeling soon, lol
Kaka x