When I lock up at night, I always find that I have to re-check it. I lock the front door, and the porch door then go to the back door to let the dogs in and lock that. But when I walk back past the front door again I have to re-check that I didn't forget to do it. I tell myself not to be silly and don't bother to re-check it and to trust myself. I don't though and I would never be able to relax until I actually go and check it. I keep checking the door is locked throughout teh day as well. I find that I tell myself 'check, just in case.' Why do I do this? Why do I have to keep checking if I've done something? Is this to do with my mental illness or is it normal?