That is normal. Their skin is loose to allow them to puff out or to pancake to increase surface area for basking. If they're just walking around, their skin will often appear to be loose but that's OK. The better indicator of hydration is to look for excess water with a poop and to watch the consistency of the urate. If it's chalky or dry or tinted orange then it may indicate dehydration. Otherwise everything is probably fine. Excess water being expelled with a poop is OK too and indicates a good level of hydration if not a little too much.