I would agree with the pp that you could have H1N1...
But I have another thought...
Could it be some sort of carbon monoxide poisoning? Headache and nausea and vomiting and napping...sounds like it could be a slow leak?
Years ago I was babysitting and someone left a burner on in the house (before I got there) and it was not lit. Totally an accident. But I got really tired, a big headache, and was about to lie down and rest - the kids were already sleeping - when my friend stopped by and smelled the gas. She freaked, we evacuated and all ended well.
I am just wondering if it could be something that maybe you would want to rule out?