Systolic Pressure

• Blood pressure is made up of two measurements. The top, or higher, number is call systolic pressure. It measures when the heart contracts. Systolic should be higher than diastolic. Laying down normally decreases systolic measurement because you are resting and more relaxed, according to Dr. Marvin Moser.
  
  

Diastolic Pressure

• Diastolic pressure is the bottom, or lower, number in a blood pressure measurement. It is when the heart rests between beats. It is generally always lower than systolic pressure. Laying down may decrease the diastolic portion of your blood pressure.
  
  

Blood Pressure Factors

• Many factors affect blood pressure. Physical factors such as heart rate, fluid volume, blood vessel size, blood thickness, posture, fatigue and even hunger can change your rate. Also stress, depression and anxiety can affect it.
  
  

Posture

• When you sit, stand or lie down, your blood pressure should change. This has to do with the effect of gravity and fluid changes. Laying down generally lowers pressure, according to the "Journal of Clinical Nursing". Even the blood pressure tool you use may have different measurements in different postures.
  
  

Right and Left Side

• If laying on your right side is comfortable and relaxing for you, it is possible that both systolic and diastolic pressure will be lower. Laying on the left side improves circulation for pregnant women.