Blood pressure readings only 10 points apart?

I suffer from extremely low blood pressure that causes lightheadedness and fainting. Recently I got BP readings that were only approx. 10 points apart (80/70, 74/65, 86/75). I can't seem to find any answers on the web related to readings that are very close together except in the cases of high blood pressure.... show more I suffer from extremely low blood pressure that causes lightheadedness and fainting. Recently I got BP readings that were only approx. 10 points apart (80/70, 74/65, 86/75). I can't seem to find any answers on the web related to readings that are very close together except in the cases of high blood pressure.
What could be causing readings to be so close together? The low pressure is no surprise to me (I have been suffering with it for almost a year and I am currently taking meds to help raise it) but the fact that the readings are so close together is bothersome. Does anyone out there know what could cause it or what exactly a close systolic and diastolic reading means?

Thanks in advance!!

PS I am currently under the care of a cardiologist and I am waiting on a call back, but I thought someone here might be able to help. My current diagnosis is POTS (postural orthostatic tachycardia syndrome)
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