Fear of losing a loved one

This thought comes to me time to time, specifically when things are actually going great in my life. All of a sudden I find myself worrying about losing my husband (like he dies or something terrible happens), the person I love the most. (I don’t have children yet). I can’t imagine life without my husband. I love him so much. My thoughts around this have no basis, my husband is a healthy, young man. I also know that I have no control over something happening to him or not. So, based on the April workbook, I am just wasting time worrying about this thought. How should I think about this? What should I be telling myself that will put me at ease? Thank you!