How do you get unwanted thoughts out of your head?

Last night I was laying down. I was really paranoid that someone was watching me through the window. Then I heard barking. But it wasn't my dog, I know because I can tell the difference between different barks and it sounded like it was right outside my door but it was subtle, it sounded like it wasn't there but it was. It was getting incredibly annoying so I tried to close my eyes and get some sleep. But images of tarantulas kept popping up in my head. So I tried to thing of other things like unicorns and docks above lakes but tarantulas kept popping up! I eventually had to get my favorite DVD and turn it up really loud and put the air conditioning on high (which is loud). That worked but I need other ways. Like what should I do if this happens and I am not at home? Thanks and no rude answers please. :)