When I got DS up this morning I noticed that his fontanelle (well, what's left of it) is quite noticably sunken. He has a slight cold at the moment - but his only symptoms are a snotty nose and a slight cough. He hasn't had a fever or shown any other signs of feeling unwell.
He has been sleeping a bit more than usual however, and where he usually wakes 2-3 times a night for feeds, last night he only woke once.

I've given DS a feed this morning, but he must have finished cause he pushed me away. I've been offering him water, but he's not interested. He seems otherwise fine - he's alert, playing happily, skin supple, etc.

Should I be worried, should I take him to the doctor? Or should I just make sure I keep offering drinks and keep an eye on him?