Have you hit 30 yet? For some reason, at about 30 I started to really consider the reality of death. I can't say i ever really worried about it in my twenties or teens. But I've heard this is fairly common.
I also noticed that by the time I was 30 I had experienced more than a fluke of young people dying.. car accidents, drug-overdoses, suicide, crime, and even occasionally from health problems. If I had any questions about my own mortality this seemed to drive the point home.
I don't think it is neccessarily OCD, alot of people report that they think of death much more when they age, or when they are exposed to people they know well passing. I have also had strange fears like what you mention from time to time.. I wouldn't even say it's a fear.. more like "oh that would happen to me, i'd be that one person in 25k to have such and such happen" .. but I think this is actually coming from my E4 trait--- meaning that 4's tend to really focus on their differences, thus they probably pick up so called "patterns" of weird shit happening to them.. but it's not really a pattern in the scheme of things.. like weird stuff probably happens to other people just as much, if not more, but the 4 sees it more. Thus they go forward convinced that weird shit is bound to happen to them.. based on this self created pattern, and might find themselves saying stuff like "I've just always had a feeling I'd die young" or "I just always had a feeling that I might not be able to have children" or "I just always have a feeling I'd end up living in a different country".. etc.
Now, if your not a 4, and your not over 28-ish, and you haven't been exposed to someone close passing, or observed some type of death incident that really impacted you, or you haven't had some type of belief system you were holding onto really challenged.. then I have no idea why you might be doing this. Hopefully someone else has good ideas.