If it is slow, speed up your exercising. If it is high, slow down. Your target heart range is only a guide. Take it easy if you feel you're overdoing it. Eventually you'll know what it feels like to be exercising in your target heart range and you won't need to take your pulse.
Physical fitness is a vital part of overall wellness.
When pursed in a balanced way, exercise such as running affects the mind and spirit as positively as the body.