When you are mindful you should be be mindful of the 4 Frame of Mindfulness. These are all tied with sensation. If you are looking at bodily posture or movement you sense this through your sense faculties. In once if comes in contact with the sense faculties you get a sensation as per dependent origination. Similarly for other frames of Mindfulness. You have to be mindful of the arising and passing away of sensations being equanimous. This has a very soothing effect.
Even a circus girl has to be mindful in order not to hurt or kill your self. This type of mindfulness does not reduce stress but creates more stress.So So you should practice the right type of mindfulness which takes you out of misery than create more misery.