Existing vs Living?

I saw something on Dr Oz today that made me think.  Are you living or are you existing?  If God forbid the worst happens to you... do you something to live for... something to hold on to?  It's a totally human thing to think about isn't it?  What is true happiness?  Is happiness sitting in front of the tv, watching everything on the television or pvr'd?  Spending time playing video games or hanging out with hubby?  Is that truly living?  Or is it just existing?  What defines existing vs living?  I feel like a teacher.. today class this is your homework.. determine whether you are existing or just living.... LOL!  Tell me your thoughts....