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.
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.
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.
worse
Yes, illnesses become worse as time goes by.
Its getting worse because people are asking questions (like this one) which are meaningless. You see we have no idea what your "problem" is from the wording of your question. This issue with people seemingly being unable to articulate their requests in a cogent manner is getting worse and worse. It is my fear that each generation is getting more and more degenerate.
Getting worse.