I Worry About Those I Love

I constantly have this perpetual fear that I'm going to lose my best friend somehow. Not through anything personal between us, but through something literally happening to him, like a car accident. There's no substance to this, right? Am I just so hugely attached to him that I'm just mortified of losing him? In all fairness, I've never had a friend I valued as much as him. We speak every day, from "good morning" to "good night". I used to have a friend I valued almost as much as him, and I had that same fear of something happening to him. Lo and behold, he's still breathing and uninjured today. I'm probably just paranoid, but getting this off my chest feels nice. It'd be nice to hear from others who have felt the same way about people before.