I echo what others have said about this being a part of Obsessive Compulsive Disorder - especially if these thoughts are intrusive.

I have intrusive thoughts of my loved one's in horrible accidents and disasters. If my son is late to a meeting with me I panic that something has happened. My daughter is late to return a call and I can't help but think something is wrong. etc.

CBT (Cognitive Behaviour Therapy) has helped with this immensely.