What are you doing when you are not doing anything?

You may say "nothing". But according to an article in TIME we are traveling in time when we are doing nothing. When our mind is not involved in any task, it travels in time. Either reviewing the past memories or foreseeing the future. The thing is that if you have some distracting memory in your head or some not very pleasant event coming in the near future, you may get even more anxious when you are idle because your mind starts exploring them.