Nighttime pressure should be more than 10 percent lower than blood pressure during the day, according to PubMed Central. With normal daily blood pressure in healthy individuals below 120/80 millimeters of mercury, nighttime blood pressure should be below 108/72 millimeters of mercury, according to the American Heart Association.
Nighttime or nocturnal blood pressure is regulated by circadian rhythm. External factors influencing circadian patterns include stress, activity and posture, while internal factors include autonomic nervous and endocrine systems, explains PubMed Central.
The nocturnal dip of 10 percent in blood pressure levels is a normal occurrence even in hypertensive patients. The lack of blood pressure decline is often observed in patients with disorders of the autonomic nervous system, essential hypertension and some forms of secondary hypertension, states PubMed Central.