The only thing between being happy or sad is the way you are feeling.
I suppose you think that is stupid but it's not.
If you really get to grips with what you are sad about you should understand that no problems are insurmountable. They usually just take one small thing you don't want to do to overcome them.
- Do it then you will no longer be sad or worry about it.
If not, I guess I'll smile for you to bring you sunshine!!