Based on a 1997 thesis by Dr. Arnon submitted in partial fulfillment of the requirements for the degree of Doctor of Sciences at the Technion–Israel Institute of Technology. Received April 5, 2000; revisions received Aug. 16, 2000, and Feb. 5 and Aug. 21, 2001; accepted Oct. 16, 2001. From the Department of Psychiatry, Rambam Medical Center and Bruce Rappaport Faculty of Medicine, and the Sleep Laboratory, Bruce Rappaport Faculty of Medicine, Technion–Israel Institute of Technology, Haifa, Israel; and the Psychology Department, University of Haifa, Haifa, Israel. Address reprint requests to Dr. Klein, Department of Psychiatry, Rambam Medical Center, Haifa, Israel; firstname.lastname@example.org (e-mail). Supported by grants from the Chief Scientist of the Israel Ministry of Health and from the Rehabilitation Department of the Israel Ministry of Defense. The authors thank H. Stein, M.D., D. Herer, M.D., C. Zinman, M.D., D. Reiss, M.D., and M. Rinot, M.D., for assistance in patient recruitment.