For the most part it is normal for a period to come eight days early. It could just be that your cycle is changing. Sometimes there are other things that may cause you to have your period early such as an infection. Most of the time it is just your cycle changing.
If you are experiencing some higher than normal stress levels, not taking care of yourself or things like that it can happen. But if it's alarming you and you don't feel like perhaps it's no big deal, listen to your body and see a doc to be sure.