It is not normal for blood pressure to be 20 mm Hg higher when lying down than when sitting.
The difference between horizontal and sitting blood pressure measurements is usually not very large, usually not more than 10 mmHg; more than 20 mmHg, the sphygmomanometer may not be located in the same position as the heart, making the blood pressure measurement not accurate enough; it may also be emotional tension and excitement, resulting in inaccurate measurement of blood pressure.
It is recommended to measure again in the sitting position, which can keep the heart at the same level as the sphygmomanometer, and the result will be more accurate. If the systolic blood pressure is greater than or equal to 140 mmHg and/or the diastolic blood pressure is greater than or equal to 90 mmHg in three measurements taken on non-simultaneous days, it meets the definition of hypertension, and there is a high likelihood that hypertension is suspected.
If hypertension is suspected, please go to the hospital promptly, have a thorough examination, and actively cooperate with your doctor to avoid adverse consequences.