Another one of the many annoying symptoms of ME/CFS is the dizziness and lightheaded feeling that we get with the illness. Some days, the dizziness can be mild and other days some patients can faint from it or come close to it. I actually did faint once years ago and I know now that it was from orthostatic intolerance due to the CFS. The doctors couldn’t explain it back then but I’ve done enough research and studied the illness enough to know that is what I experienced and what I still experience today. I haven’t fainted anymore since that one time but I have felt like I was going to many times and I experience the lightheadness and dizziness on a daily basis.
I found a great 27-page PDF from the CFIDS Association on orthostatic intolerance titled General Information Brochure On Orthostatic Intolerance & Its Treatment. It explains in great detail and length what exactly orthostatic intolerance is and here is a little excerpt:
Orthostatic intolerance is an umbrella term for several conditions in which symptoms are made worse by upright posture and improve with recumbency. This document provides further information about neurally mediated hypotension (NMH) and postural tachycardia syndrome (POTS), two common forms of chronic orthostatic intolerance. Hypotension is the medical term for low blood pressure (BP), and tachycardia is the medical term for an increased heart rate (HR).
What are NMH and POTS?
Neurally mediated hypotension refers to a drop in blood pressure that occurs after being upright. We define NMH by a drop in systolic BP of 25 mm Hg (compared to the BP measured when the person is lying flat) during standing or upright tilt table testing. Although NMH may be slightly more common in people with a low resting blood pressure, most people who develop NMH during standing have a normal resting blood pressure. NMH is an abnormality in the regulation of blood pressure during upright posture. It occurs if too little blood circulates back to the heart when people are upright, a situation that can trigger an abnormal reflex interaction between the heart and the brain that results in a lowering of blood pressure. NMH is sometimes known by the following names: the fainting reflex, delayed orthostatic hypotension, neurocardiogenic syncope, vasodepressor syncope, vaso-vagal syncope. Syncope is the medical term for fainting.
Postural tachycardia syndrome refers to an exaggerated increase in heart rate with standing. A healthy individual usually has a slight increase in heart rate—by about 10-15 beats per minute—within the first 10 minutes of standing. POTS is considered present if the heart rate increases by 30 beats per minute, or if it reaches 120 beats per minute or higher over the first 10 minutes of standing, accompanied by orthostatic symptoms. POTS is an abnormality in the regulation of heart rate; the heart itself is usually normal. Some patients with POTS in the first 10 minutes of upright standing or tilt testing will go on to develop NMH if the test is continued; the two conditions often are found together, and they are not mutually exclusive diagnoses.