Pure autonomic failure (PAF) is a neurodegenerative disease of the autonomic nervous system, which regulates body processes like blood pressure and breathing rate. PAF usually affects only the peripheral autonomic nervous system, which means it does not usually involve the brain and spinal cord (the central nervous system). Symptoms begin in midlife, although they can begin earlier. The main symptom of PAF is orthostatic hypotension, a sudden drop in blood pressure upon standing. This can cause dizziness, lightheadedness, blurry vision, and weakness. Other symptoms can include fatigue, bladder problems, constipation, abnormal sweating, and sleep disorders. The symptoms of PAF tend to get worse over time, and sometimes, PAF can lead to other conditions such as Parkinson's disease, dementia with Lewy bodies, or multiple system atrophy. The cause of PAF is not known. The symptoms are caused by abnormal accumulations of protein, called Lewy bodies, in the cells of autonomic nerves. The Lewy bodies restrict the production and release of norepinephrine from nerve cells, which in turn causes hypotension. Diagnosis of PAF is based on the symptoms, clinical examination, and a thorough neurological examination. Testing may involve tilt table testing, 24-hour blood pressure monitoring, hyperventilation testing, and a norepinephrine blood test.