Checking her temperature is a good idea and give her a little bit of panadol if it is raised as this will help to lower it. She may well be coming down with a bit of a bug or a cold or something like that.

Like Kirsty said, I'd let her sleep if that's what she needs to do. If she's a bit unwell, she needs that extra sleep to help fight off whatever little nasty she has brewing. Whilst she's awake, keep offering her the boob to push the fluids and nutrients through.

When in doubt, a visit to the GP is always in order! Even if it's just to reassure you and the GP says she is fine!