A second sleep study will be used to accomplish this second objective. Using precise methods, we will quantify the prevalence of IFL during sleep in GWS patients and in Gulf War veteran controls. Following completion, each study will be staged using Rechtschaffen and Kales criteria. From each study, 3 three minute periods of continuous NREM sleep (a total of approximately 120 breaths) will be randomly selected and analyzed for the prevalence of flow limited breaths. During the three minute periods, all of the breaths will be analyzed whether they occur during sleep or during brief (< 15 second) arousals.