Amongst the many factors that lead to high blood pressure like smoking, alcohol intake, obesity, diabetes, insulin resistance etc, stress seems to be a major player in precipitating high blood pressure.  Although stress is universal, individual responses to stress are different for eg. You have the Type A personality, highly pressure prone and totally work oriented.  He or she is usually aggressive, short-tempered, with a capacity to work more than others.  He/She is not interested in any fun-loving activity and considers it a waste of time.  He/She is always striving to be rewarded and noticed.  He not only is a hard worker but also drives people around him to deliver and enjoys being internally stressed.  Such a person is usually more prone to develop hypertension than a relatively easy going person.
Stress will cause high blood pressure in a stress sensitive person if he is exposed to such conditions over a prolonged period of time.  The blood vessels get constricted as a response to stress and this constriction causes the blood pressure to rise.
One way to combat mental stress is to meditate, take a holiday or to simply relax.  Think of what the poet Thomas Gray said “The paths of glory lead but to the grave”:  You must know your limitations and try to balance your life accordingly.
Pranayam or simple breathing exercises can also help you to lower your blood pressure, calm a racing heart and also help improve your digestion.  Breathing has direct connections to emotional states and moods.  You will notice that when you are angry or afraid your breathing becomes rapid and irregular.  At such times of stress, if you voluntarily breathe slow, deep and regular, you will prevent a rise in pressure.  The way to do this is close your eyes for a few minutes and divert your attention to your breath. You can do it in any position.  First exhale completely through your mouth making a susshhhh sound. Now close your mouth and inhale through your nose mentally counting upto 4. Now hold your breath counting seven, then exhale through your mouth counting eight.  This is one breath cycle.  Repeat this cycle four times.  You will experience a certain calm coming all over you, especially in the head.  This breathing exercise is a natural tranquillizer for the nervous system.  It will even help those suffering from insomnia.
Try not to have your attention on your thoughts since they are the source of most of your anxieties.  By shifting your focus on your breathing, you will be able to relax naturally.  You can repeat this exercise several times in a day while sitting in your office chair or when in a lying down position or even when faced with a stressful situation.  It will definitely help to calm you down.