If he is not moving, cold, or things like that.
If a mouse seems lethargic or thin, or its coat is suddenly ragged and uncared for, that usually means something is wrong. Another big sign is snuffling or wheezing--healthy mice don't make noises when they breathe.
You can find more information here: http://fancymice.info/healthfrontpage.htm.
No, but due to the nature of mice to cuddle up when asleep, the other mouse will get sick as well.
yes
Possibly, yes. They occasionally canniblize.
It is not obligatory if the mouse was not infected.
You shouldn't feed pizza to a mouse, it has a lot of fat in it and it can make it sick.
No he/she mite get sick
Yes.
gross but yes
Yes.
rock it in the grill
Signs that a laboratory mouse may be sick include lethargy, hunched posture, reduced appetite, weight loss, respiratory distress, and abnormal behavior. Regular health monitoring and observations of physical symptoms can help identify illness in mice. Consulting a veterinarian for a thorough examination and diagnosis is recommended if a mouse is suspected to be sick.
no it just needs to drink more