Weird mood/Depressed for no reason?

I dont really know how to explain this at all. But recently, I've been feeling down. It's really strange, like the things I think about. I feel like there's so many people out there in the world my life seems so small in that aspect. I know this sounds weird, but I've been thinking about how i want to live my life, like there are so many things I want to do, I want to make my life the best it can be. I know that part sounds hopeful, but at the same time it brings me a weird depression for some odd reason. I think I should maybe start immersing myself in things I enjoy again. I know this sounds really weird, but if anyone can help it'd be greatly appreciated :]