A largely mysterious condition that reportedly afflicts as many as 17 million people worldwide, Chronic Fatigue Syndrome still flummoxes most physicians, and remains frequently dismissed as a psychosomatic “illness” — including by some nations. Still, it’s hard to buy the “all in your head” diagnosis when seeing the long-term, sometimes entirely bedridden victims of CFS in “Unrest.” Director Jennifer Brea is one of them herself, and this first-feature documentary chronicles her own struggles while taking in the perspectives of other patients and experts around the globe. Though the “Patient, film thyself” concept is starting to risk overexposure — Sundance alone premieres two such features this year, the other being ALS-themed “It’s Not Dark Yet” — “Unrest” is a high-grade example of the form that’s consistently involving, with content diverse enough to avoid the tunnel-visioned pitfalls of diarist cinema.

Narrating her own tale of drastic, inexplicable loss (medical science still doesn’t know what causes CFS) and necessarily sporadic attempts to fight back, Brea starts out by painting a picture of the person she used to be: an inveterate world traveler, among other things, interested in sampling every culture and experience. Educated at Harvard and Princeton, she found a like-minded soulmate in Kenya-born internet analyst, social-network pioneer and Princeton professor Omar Wasow, whom she married. But three years later, at age 28, after contracting a fever of nearly 105, she began to experience a never-ending panoply of symptoms including extreme exhaustion, numbness, acute pain, uncontrolled movement, and extreme sensitivity to light and noise. Seeing umpteen specialists, she was at first told she must just be physically manifesting a delayed psychological reaction to “some distant trauma” she might not even remember.

But eventually she discovered a whole hidden community of “the missing” — others who had basically lost all normal life functions to the condition some prefer now to term Myalgic Encephalomyelitis, or ME. Among those given a podium here (through both Skype chats and location footage principally from the documentary’s two d.p.’s) are Georgia housewife Leeray, whose husband left her because he thought he was acting as a “crutch” for an imaginary illness. (A decade later, he stopped doubting when one of their daughters also got the illness.) The son of Stanford genetics professor Ron Davis is so diminished that he’s been unable to speak, let alone leave his bed, for more than a year when we meet him.

The most alarming case is that of Danish teen Karina Hansen, whose parents were horrified when police virtually raided their home and forcibly removed her to a state facility — because Denmark is one of the countries that categorizes CFS as a psychiatric condition, and thus considered her a “captive” who was not getting proper treatment. (Incredibly, it took three years of protest before she was released, with no improvement.) The questionable reason that government doctor Per Fink offers for tearing families apart is that viewing CFS as strictly psychological is “more interesting” to him.

As for Brea — she’s first seen unable even to lift herself from the floor, though her condition is variable. She has good periods usually followed by long, hard crashes into pain and dead weariness. Patients are shown to have come up with numerous home-remedy “cures” (most of a dietary nature), most of which have fleeting impact at best. More successful are Brea’s efforts at orchestrating heightened awareness for a syndrome that still attracts considerable public skepticism, and whose medical research is poorly funded as a result. Through it all, she has the unconditional support of husband Wasow, though in darker moments she agonizes that she’s ruined his high-achieving life by handing him a caregiver role he insists he does not resent.

Proceeding at a measured pace — no film about Chronic Fatigue Syndrome should be over-energetic — “Unrest” ably juggles content that’s wide-ranging enough in tone, style and information to prevent the film over-dwelling on Brea’s personal laments. It’s gracefully edited by Kim Roberts and Emiliano Battista, with Bear McCreary contributing an affecting, string-based score.