One of the most difficult things to learn is that mindfulness is not dependent on any emotional or mental state. We have certain images of meditation. Meditation is something done in quiet caves by tranquil people who move slowly. Those are training conditions. They are set up to foster concentration and to learn the skill of mindfulness. Once you have learned that skill, however, you can dispense with the training restrictions, and you should. You don't need to move at a snail's pace to be mindful. You don't even need to be calm. You can be mindful while solving problems in intensive calculus. You can be mindful in the middle of a football scrimmage. You can be mindful in the midst of a raging fury. Mental and physical activities are no bar to mindfulness. If you find your mind extremely active, then simply observe the nature and degree of that activity. It is just a part of the passing show within.
--Henepola Gunaratana, Mindfulness in Plain English from Everyday Mind, edited by Jean Smith