In fact, talking to yourself can be a great way to interpret something that you are thinking about. For example, if you are reading something, it will help you understand what you are reading to speak the words out loud. This is because you are using more of your brain to process what is being read and you will also interpret it differently if you hear the words vs just seeing them.
A lot of (if not all) people talk to themselves. talking to yourself in itself is normal and healthy, but if you have a concern, think about what you are saying. It could help you see what isn't healthy.
Check out this website for more information http://healthmad.com/mental-health/talking-to-yourself-is-it-normal/
The DSM-IV is the authority of mental illness in America.