How do you tell if you're having intrusive/obsessive thoughts, delusions or whether this is something else? I have a bunch of things I believe in that I'm beginning to realise are odd, like that:

• There are cameras hidden around my house/people are watching me (including people/animals in photographs and pictures, and toys)
• There are people in my room or house that will kill me if I'm not constantly on guard, or that my family members are going to get killed so I have to constantly watch over them.
• Horror story-like things are about to happen to me (although I don't believe in supernatural things otherwise), such as my reflection in the mirror being a ghost/demon or being dead (or something else that's very scary)
• If I think of other people, they'll be able to see where I am and what I'm doing. Sometimes I think that people can read my mind, though this one is less common and easier to dismiss.

They seem to be much more than normal beliefs, and although I can't logically support the beliefs, I completely believe in them even if I tell myself they're not true. They've resulted in me going to bed convinced that I'm going to be killed or will never wake up again, and are just generally creepy and very scary to experience.
I don't think I wrote this in the best way to explain just how weird this all is. I'll elaborate on this if needed, since there are some other things attached to this that aren't exactly normal, but I can't think what else to write right now. (I didn't know where to post this so sorry if it's in the wrong place).

Any help would be great.
Thanks.