There is a simple diagnostic procedure to determine low blood volume. It involves taking what are called orthostatic vital signs. There are lots of missing pieces to this story. I suspect you were dehydrated. There is a communication problem between you and your physician. As Drnee stated: "the cause must be known for proper treatment". I would go back to your family physician and share your concerns.
Hi
Welcome to the forum!
Maybe you mean low blood pressure. Without proper investigations it is not possible to comment on the cause.
You could be having probably postural hypotension. The blood pressure falls when you stand and causes all the symptoms that you are suffering. Dehydration, certain medications, heart problems, untreated diabetes, and nervous system disorders can all cause this. Blood pressure monitoring, tilt table test, EKG, heart echo, ambulatory blood pressure recording are all required.
Hypothyroidism, hyperthyroidism, Addisons’ disease, hypoglycemia, VitB12 and folate deficiency can all cause hypotension.
The cause needs to be known for proper treatment. Otherwise any treatment will raise the blood pressure.
Hope this helps. It is difficult to comment beyond this at this stage. Do discuss this with your doctor. Please let me know if there is any thing else and do keep me posted. Take care!