 In Specific Aim 1, the investigators will use state-of-the-art measurements of sympathetic activity autonomic function tests, response to trimethaphan, direct nerve sympathetic traffic recordings with microneurography, plasma norepinephrine, and intraneuronal metabolites, inflammatory mediators C-reactive protein, inflammatory cytokines, and oxidative stress isoprostanes in patients with CFS-P. It is important that appropriate control groups be included, and we will also study patients with CFS without orthostatic tachycardia, patients with POTS without CFS, and normal controls. 