A common cause of dizziness, light-headedness, and fainting is a low blood pressure that occurs when a patient stands up. This low blood pressure can be the result of medicines taken for high blood pressure or for Parkinsons Disease. Other types of medicines can also cause a too low blood pressure when standing.
Because doctors don’t usually take blood pressures of patients while standing up, this problem (a low blood pressure while standing [called orthostatic hypotension]) may not be detected.
But you can check your own blood pressure and pulse lying down and standing up with your home blood pressure machine.
Have the person you are checking lie down on the sofa or bed for 5 minutes and then measure the pulse and blood pressure while the person is lying down. Then, help the patient stand up and recheck the blood pressure and pulse within three minutes of the patient standing up.
An abnormal result is the drop in the systolic blood pressure (the top number) of 20 mm Hg or more or a drop of the diastolic blood pressure (the bottom number) of 10 mm Hg or more and is called orthostatic hypotension.
It is also abnormal if the heart rate increases by 20 beats per minute or more and is called orthostatic tachycardia.
Orthostatic hypotension (an abnormal blood pressure while standing) and orthostatic tachycardia (an abnormal increase in the heart rate) can be an acute problem caused by infection, dehydration, or blood loss from internal or external bleeding.
Thus measuring the orthostatic (supine and standing) vital signs can give you and the doctor an early clue that something serious is going on in a child or adult.
Orthostatic changes are common in older adults due to medicines and also due to autonomic nervous system changes from aging or from diseases such as diabetes. In older adults the changes can also be due to infection, dehydration or blood loss.
The reference below is excellent. (1)
(1) Sclater A, Alagiakrishnan K. Orthostatic hypotension: A primary care primer for assessment
and treatment. Geriatrics 2004; 59(Aug):22-27 available at https://academic.regis.edu/clinicaleducation/pdf’s/Orthostatic_Primer.pdf.