for healthy adult humans, the systolic blood pressure should be below 120, and the diastolic blood pressure should be below 80. however, blood pressure can be very different for each person. blood pressure also changes naturally during the day (in a circadian rhythm). it gets lower during sleep and gets higher when a person gets up. it is lower when a person is resting and higher during activity. many other things - like stress, disease, drugs, and what a person eats - can change blood pressure. even the stress of having blood pressure taken can make it higher. this is called "white coat hypertension."