I'm so sick of being scared!

I'm not a little girl so why does every little noise in the dark make me think someone is going to come and kill me??? I HATE IT!!!
I just can't do this anymore. It's so stressful being scared all the time, and I don't even know the cause and I just want to get better but I can't! -.-
If not knowing what happened is supposed to protect me why am I not feeling protected??? Why do I have to feel so terrified and unsafe? I wish I could just chase away the monsters from my/our past. I wish I could remind myself that I'm in the present, that nothing's going to happen.
Why am I so sure someone is going to break into our locked secure apartment and will kill me???
I feel like breaking down right now :'( just so fed up with feeling like this