What if the person closest to you was the devil in disguise?

Like I try so hard to be a good person. But I do occasionally have really bad thoughts. And I don't know why they happen or where they come from. I heard theyre intrusive thoughts. But I read a lot of the news, articles everyday. And someone just snaps and ends up killing their whole family or friends. When they used to be a good person. How does a good person turn evil and twisted so suddenly. I would often think to myself. Will I turn evil one day. But it's not my nature. I rather kill myself then have anyone hurt. But when I'm angry I have trouble controlling myself and my emotions. So I take mood stabilizers. It happens everyday. The person you knew yesterday is not the same person today. And that is a scary thought.