Well they're related. Although fear tends to have an element of aversion in it. Whereas worry we can just be thinking about what we have to do over and over rather than being afraid about it. Usually fear is a bit stronger, whereas worry can be just "Am I going to be able to remember everything I have to do?," or "What am I going to do there or what am I going to do here?," and all these sorts of concerns we may have about what we're going to do and where we're going to go and how much we have to do, etc. Whereas fear tends to be, as I said, an element of aversion, a wishing for anything that we're thinking about not to happen, and it tends to have a bit of a stronger energy. So if you have an inkling, it's fear, just try to note, "fear, fear," if you have an inkling it's worry, just try to note, "worry, worry." And if you can't actually distinguish between the two then it doesn't really matter, you can say fear or worry. Try to see it in the body, try to have compassion for yourself, and it may be helpful to have a balancing Reflection on Death at that particular moment to understand that none of it may come about anyway.