I am more familiar with POTS than with NMH, but it seems you might have NMH. According to the paper of Robertson 2008 “The pathophysiology and diagnosis of orthostatic hypotension” (http://mc.vanderbilt.edu/gcrc/aas/CA...0Robertson.pdf ):

“Orthostatic hypotension is defined as a fall of systolic blood pressure of at least 20 mmHg or a fall of diastolic blood pressure of at least 10 mmHg within 3 minutes of standing”

My POTS is cyclic, some days are better and some are worse. If you measure your BP when you have the symptoms you might get larger reduction of BP.

When standing the blood pools in the lower part of the body. The autonomic system regulates the contraction of the blood vessels, the HR, BP etc., so enough blood will reach the brain.
SFN can affect the autonomic nerve fibers and when the amount of blood reaching the brain is too low, it can cause symptoms such as seeing black spots (or losing the vision for a couple of seconds), feeling dizzy, brain fog, breathless etc..

Being in high temperature (Hot weather, hot shower..) or drinking alcohol cause a dilation of the blood vessels and makes the symptoms worse.

Increasing blood volume by high salt and water intake can increase the BP and help the symptoms. It is better to get the diagnosis and consult your doctor before trying it.

I have similar pain. I think my pain involves my Sciatic Nerve....Doctors couldn't say for sure. I've been taking Gabapentin aka Nerontin (600 mg 3 times a day). and it has made a positive change. My pain often starts because I sit too long with pressure on the back of my thigh. When that happens I take the Gabapentin then walk around until the numbness/tingling in my foot is gone. :cool: