I've been lurking and meant to register and introduce myself but never quite got around to it. However Civet's problem is something I've experienced a lot so I thought maybe I might have something useful to add. I'll try and get around to introducing myself later but I don't tend to have much time or enthusiam for web boards at the moment so you may not hear much from me.
For background to this issue - when I was a teenager, I was so afraid of my house being broken into that I couldn't sleep in my own bed, even if my brother was in the next room and my mother on the other side of the house. For some months (maybe over a year, I can't quite remember) I even had to sleep in my mother's bed (yes, with my mother there as well). During the day, I couldn't stay in the house alone even for a few minutes without barricading myself in the bathroom with a cricket bat.
Now I live alone and only occasionally have relapses, like last year when I received a threatening phone call (it was a death threat but think I was just a random dial). I needed my mother to spend a few days in my spare room so I could settle down and then I booby-trapped the house for a few months (eg things that would fall off the door if it was opened).
So this is the background to where my opinion on this comes from. The other thing I should add is that while I never had that problem treated, I've had to get treatment for other anxiety issues and some of what I say comes from this experience.
I agreed that it is a good idea to review the security at your house and see if there is any obvious issue, and I think it is a good idea to do a few things that make you feel better. Things that helped me were putting noisy things on the back of doors that would fall off if the door was opened (including my bedroom door which might be an option for you Civet), having an ornamental sword by my bed and having 2 phones by my bed. With the ornamental sword - it wasn't much use as a weapon, but I reasoned that if someone did break in, they would get one awful fright if confonted by a shrieking, sword-wielding lunatic.
However there is also a danger that you can "validate" your fear by acting on it. For example, if you put noisy things on the back of every door before you go to bed and eventually get off to sleep after lying there for hours with your pulse racing and then wake up and it is all fine, then the next night you think - I must booby trap every door before I go to bed and it will be ok. Pretty soon you can't bring yourself to go to bed without doing a whole lot of odd things. Or worse you need to keep adding more things. Or you can't sleep in your bed/ home at all. Been there. Don't recommend it.
So the other thing I did was focus deliberately on the "but it isn't likely" rationale. I reminded myself of things like "I have nice but nosy neighbours", "my house is inconvenient to break into" etc. I avoided imagining burglars or anything else that might make me more anxious (usually by replacing with some other thoughts, something pleasant and obsessive). Also I reminded myself - "see, the booby traps weren't necessary after all" when I woke up in the morning rather than saying "it was ok because I put the booby traps up and had 2 telephones and a sword by my bed". From my understanding of phobia treatment, these subtle differences are important.
Eventually, I was able to dismantle the booby traps etc.
Anyway, I don't think you are paranoid at all - it is a quite reasonable fear, but it is also really miserable if it gets hold of you, and it isn't helping you. It doesn't make you more secure that you are afraid. For me thinking about the fact that "this fear is unhelpful", helps me to put the anxious thoughts to one side. Don't know if it helps you but worth a try.
So, that's my incoherent late-night rambling. I hope I don't come across as bossy (I know I can sometimes). If you want me to explain more, I'll try. If this is no help, just ignore it, but I just want to try to help you because I really think I understand what you are experiencing.
And, um, hi everyone.