Goodbye..?

I don't know anymore. Is this the end? I wonder, how can people get old? How can you live healthy? How can you be happy for a long time? Does happiness really exist?
I feel like this is the end. Nobody notices it. But how do you write a goodbye note? Where do you leave it for your family, when do you send it to your friends, should you even do that, or should you just let them notice?
My so called friends wouldn't notice, my mom would probably try to wake me up if my body would still be here, but I don't know... What do you do when the end is near? How do you leave?