We always talk about being "present" in Yoga. Being in the moment and letting go of past and future. The brain is so amazing in that it helps us remember things, think and also controls our physiological processes. The brain juggles all these important tasks and is constantly multi-tasking. This is why its important to stay present. In order to give our minds a break from the juggling. Getting stuck or being heavy in our past is a common issue. Or anticipating the future to the point that it creates anxiety or stress. These are things we all commonly do and while our brains are trying to manage these thoughts, we might be putting a little less energy into our important physiological processes like digestion or resting and healing.
Sometimes when we get caught up in worrying or dwelling, we forget to live in the present and be in the moment. More importantly we forget to enjoy that present moment. Our lives are a process. Our Yoga practice is a journey. There are difficult times and bumps in the road but its all part of the work to bring you forward. We have to go through these things anyway, we can only make it easier on ourselves if we decide to find joy in that. Next time someone asks you told hold utkatasana/chair pose for 5 breaths...just curl up the corners of your mouth and find the joy in it. You will find that the 5 breaths will be over much faster than you think!
Take it from Deepak