According to the diagnostic criteria for blood pressure, a blood pressure of 91/55 mmHg is not normal because the normal systolic blood pressure in a healthy person is between 90-140 mmHg, while the diastolic blood pressure is between 60-90 mmHg, so a systolic blood pressure of 91 mmHg is in the normal range, at the lower limit of normal, while a diastolic blood pressure of 55 mmHg is below the normal range. If this blood pressure value occurs while the patient does not have any uncomfortable symptoms, there is no need to be overly nervous and just keep a close eye on the blood pressure. However, for middle-aged and elderly patients who have had high blood pressure for a long time and have been taking medications for a long time, this blood pressure value may be on the low side and the patient may experience symptoms such as peripheral weakness, dizziness or even blurred vision, etc. It is necessary to adjust the antihypertensive medication on the basis of monitoring the blood pressure, either by using weaker antihypertensive medication or suspending the use of medication to bring the blood pressure back up to a certain extent and alleviate the symptoms.