People with POTS, autoimmune autonomic neuropathy (AAN), pure autonomic failure (PAF), SFN and Ehlers Danlos Syndrome (EDS) do not only suffer from orthostatic symptoms such as dizziness, headache, neck pain, blurred vision or (pre-) syncope. They also experience deficits in attention and concentration (more precisely deficits in selective perspective, operating speed, executive functions and memory performance) mainly in upright position. Only few studies concerning cognitive impairment in autonomic neuropathies, their frequency, aetiology and therapy exist. Many patients concerned, especially with POTS, report attention deficits and "brain fog" with problems in their everyday life and work, predominantly in upright posture. Specific symptomatic or medical therapies do not exist. Medical treatment with Modafinil is discussed and part of a current study at Vanderbilt Autonomic Dysfunction Centre (1-5). The investigators want to investigate if problems of concentration, attention and/or cognitive dysfunction exist in people with POTS, AAN, SFN and EDS compared to healthy controls (HC). Thus the investigators use detailed clinical, autonomic and neuropsychological tests in different body positions (lying, sitting and standing) as also acute therapy (leg crossing).

We are still recruting healthy controls and patients with autoimmune autonomic neuropathy in order to perform titl table examination and laboratory testing on day one, ono an empty stomach, without morning medication. Cognitive testing is performed on day two after randomization in three groups: lying, standing and standing with legs crossed.

Inclusion Criteria:

• AAN, SFN, hEDS, POTS or healthy control
• diagnosis in our clinic on the basis of anamnesis, clinical data as neurological examination, tilt table, QST, skin biopsy, norepinephrine values, vitamine B12, antibodies

Exclusion Criteria:

for all participants

• pregnancy, nonage,severe heart insufficiency, deep brain Stimulation, pace maker, drug consumption, large fibre polyneuropathy for controls
• medication influencing blood pressure, psychiatric disease, synkopes or dizziness, neurological disorders esp. polyneuropathy, dementia, vitamine or iron deficiency