Unless there is a sequel, “Unrest” is probably the only film Jennifer Brea will ever direct. That’s because she has severe myalgic encephalomyelitis, or chronic fatigue syndrome, and her movie — which opens Friday, Sept. 29, at the Vogue Theatre in San Francisco and the Rialto Cinemas Elmwood in Berkeley is an unflinching look at her battle with the disease, and the millions of people around the world — about a million in the United States — who are afflicted, with many essentially bedridden for the rest of their lives. Brea was a Ph.D candidate at Harvard and newly married when she suddenly developed a fever, her temperature as high as 114 degrees.