The more these thoughts scare you and the more you try not to think about them, the more you will. It's a bit like my telling you not to think about a purple elephant for the nest 30 seconds, all you will be able to think about is a purple elephant. The important thing is that you realise that you're having these thoughts. A serial killer probably wouldn't be distressed at thoughts to them it would be 'normal'. It's just anxiety that's causing it. Have you considered medication to help?
Lisa x