Please help! Panic attacks?

I'm always thinking things like what if the sun explodes right now and stuff and I get that panic feeling and I don't know what to do about this.. I'm paranoid about the world ending and things like what if there is no heaven and once we're dead, we're dead, there's no after-life or anything. Please help I don't know what to do. I think I have OCD if that's what this could be then at least I know what it is but if it's not the OCD then what is it? should I talk to my doctor or what? Do you ever think things like this? I think them almost constantly and I don't know how to stop:( Please help I'm really scared:(