I don't know if I can help you much myself, as I have fears like this myself. Whenever I take out the trash I swear I can see someone watching me or that something is going to attack me. I also have fears of people watching me through the windows in my house or that someone is in my house, it can get so bad that I can get panic/anxiety attacks fearing that something is going to harm me. I also have fears that there are cameras watching me at times. I think can be in part of how you are raised and what messages were being told, like my grandma would warn me about people watching me from the window and it just evolved to believing someone was out there always watching me (even though I lived on the second floor) so that might be why you have your fears?