Telling people how worried you are may give you an excuse to cancel something. It also can be used as an excuse for doing something poorly.
Worry may be a way to try to connect with people. You may have the mistaken idea that if you worry about someone, that means you love them, and if you don't worry, then you must not really care.
Worry may make you feel powerful because at least when you worry — and make sure other people know you are worrying — you feel like you're doing something.
Worry can be a habit, and you may be unaware of how much time you give to ruminating about possible scary events. One could call it a form of self-harassment.
That is why it is important to pay attention to the chatter going on in your mind and to notice the feelings that are being generated by your thoughts, because carrying around those anxious thoughts may make you prone to physical ailments, such as headaches, muscle spasms and gastrointestinal problems.
In order to calm yourself, you may begin to abuse alcohol or prescription drugs, or engage in compulsive behaviors such as eating disorders, gambling, workaholism or sex addiction. While that may provide some temporary relief, when “the fix” wears off, you're back to the worrying and that sets you up to abuse again.
Worry keeps you from thinking clearly and wastes time. It does not help you find solutions and can become a substitute for taking action.
Telling someone not to worry does not make that happen (unless one promises to remedy the problem, and is able to do that.) The person may still have the strong feeling that constantly thinking of the worst that could happen seemingly has some magical power to stave it off, compared to not thinking about it.
This is completely curable, and very rapidly so. See the article on "Unseen Therapist Within."