Answer:
I belong to everyone. Sometimes make you happy sometimes make you sad. I will never end until the day you do.
I'm simple for a few people, but hard for them to hear. I live inside of secrets and bring people's worst fears. What am I?
I go up but never come down. What am I?
What runs but never walks has a mouth but never talks has a head but never weeps has a bed but never sleeps?
I come with a train and go with a train and the train doesn't need me but can't go without me.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?