I'm feel like everything is weird and different?

Well it's the start of summer and for the last few days I really haven't felt like myself. I've been thinking that I'm thinking too much and it's like i'm trapped inside my head. I can't get away from it and I try to keep myself distracted so I won't think about it. It's not like there's something bothering me and I can't stop thinking about it. It's just I can't stop thinking that i'm thinking too much, yea I don't get it either. It's really getting me down and everything feels weird and abnormal. It has never happened and i'm usually relaxed and just live life but now I'm thinking that I won't be able to stop this and my life will be a constant battle of I really don't know what. I don't get this at all, please answer if you do!!