Just ride with that feeling, never try to change it nor hate it. It will be gone in a while, all you need to do is embrace it and just stay relax.
Don't take actions if you need to, if you need to stay still then stay still. But don't ever try to force feeling some other emotions because it will make your situation even worse, you will only get frustrated once a positive feeling is not showing up on your system.
If you're feeling sad then just feel sad, don't fight it, don't make dramas, don't do anything that will make the feeling stronger. Just ride with it and never try to get sympathy from other people, never broadcast to the world that you are sad because that will only make the sadness stronger.
Any emotion will go away, no emotion will stay forever. Just be ok with feeling bad or feeling good, any emotion is no different from another, it's just an emotion... it can kill you or make you stronger. It depends on what is your approach and what you are thinking of. Just ride with that feeling until it go away... happiness is always on its way.