Measuring blood pressure at night is important because nighttime blood pressure can reveal risks that daytime readings may miss.

Normally, blood pressure drops during sleep by about 10–20%, called “nighttime dipping.” When blood pressure does not drop enough, or rises at night, it may indicate higher cardiovascular risk. 

The key reasons:

1. It can find hidden hypertension
   Some people have normal daytime or clinic blood pressure but high blood pressure during sleep. This is called nocturnal hypertension or masked nighttime hypertension. Daytime checks alone may miss it. 
2. Nighttime blood pressure is strongly linked to heart and stroke risk
   Studies show higher nighttime systolic blood pressure is associated with greater risk of cardiovascular events, sometimes more strongly than daytime readings. 
3. It shows whether the heart is resting properly
   Sleep should be a recovery period for the heart and blood vessels. If blood pressure stays high at night, the cardiovascular system may remain under pressure for 24 hours.
4. It helps doctors understand medication effect
   Night readings can show whether blood pressure medicine is lasting through the night or whether treatment timing needs adjustment. This should always be discussed with a healthcare professional.
5. It may reveal sleep-related problems
   Poor sleep, sleep apnea, stress, and other conditions can affect nighttime blood pressure. Night monitoring gives a better picture of the relationship between sleep and cardiovascular health.