Getting plenty of rest will help to build your immune system to fight the sickness faster. Your body repairs and rejuvenates while you sleep.
Yes you can. You can get MUCH worse than it already is. 
The typical antonym for better, is worse. However it can also be - more ill, sicker, unhealthy, bad, detestable, disagreeable or unpleasant.
Sadly it is getting worse in the whole world.
deteriorating
its getting worse
worse.
Depends on what you define as gun violence and where you look. Subjectively: It is getting worse in UK, despite near-total gun ban. It is not getting worse in US.
Washing your hair when you have a head cold and staying indoors will not necessarily make you sicker. A head cold is caused by a viral infection, not by getting your hair wet. However, exposing yourself to cold temperatures or drafts after washing your hair could potentially make your symptoms feel worse temporarily due to the sensation of cold on your head. It is always important to keep warm and rest when you have a cold to help your body recover.
worse
media
Getting worse.
Yes, illnesses become worse as time goes by.