How do i know my baby is sick?

Does he behave differently? A little, but something far more unexpected ..HE SLEEPS THROUGH THE NIGHT.. well well, let's not get ahead of ourselves Adri. I'm still co-sleeping with wanting to transition onto his bed due to lack of space.I took Lucas in on friday because he had a serious cough followed by vomit, the doctor said it was mild pneumonia and wanted to keep an eye on it.He was prescribed some anti-biotics and basically a free pass on the whole No-tears approach momma is trying to get him back into his bed. Well Friday night to my surprise we only woke up with coughs not wanting to feed although I know it probably has to do with his body protecting him and wanting more rest outa him. Still, not being woken up to feed is quite a shock. I'd think that if he was sick i'd be up literally ALL night!. Last night he slept 5 whole hours un interrupted followed by a small feeding then back to sleep until 7:30 am when the cough-vomit began again. Not sure if we'll make a habit out of this wonderful sleep but all I want is for him to get better.