Some of the patients interviewed in Brea's film have seen 20 doctors or more before getting a diagnosis.
One, 22-year-old Jessica Taylor of Rochester, England, one of the patients followed in Brea's film, contracted a virus at the age of 14 and has never recovered.
"I tried to keep going and tried not to let it affect me because I wanted to be well and do all the normal things kids do," Taylor said. "I had no time to be ill."
She spent months at a time in the hospital being fed by a gastric tube.
"I am one of the most severe cases," she told ABCNews.com. "All that time I have been bedridden completely and so I have not walked since 2006. At the moment I am stuck in the world of one room in a hospital bed at home."
Taylor said she has "stabbing pain like having hot needles pressed" into her legs and arms -- "all the time." Her muscles don't work, and she often has "brain fog" and can't process information. "Sometimes I try to speak and nothing comes out," she said.
"When I am listening to people sometimes they sound like they are speaking a foreign language."
She said it took her an entire day of rest to prepare for the phone call from ABCNews.com. Fortunately, her iPad has allowed her to communicate with friends and to participate in the film. She recently filmed herself sitting on the edge of the bed for the first time in eight years.
"Being tired is not near to what I feel every day," she said. "It's beyond tiredness. It's in every cell of my body -- a force so strong that it prevents me from doing everything and affects every aspect of my life."
Running a charity to benefit children and young adults with illness from her bed --- Share a Star – is what keeps Taylor going. "When you are stuck not able to do a lot of things, you get a real desire to push on and really make something in the world."
As for Brea, she has seen some improvement with an immunomodulator, magnesium injections and dozens of nutritional supplements. Despite her illness, she hopes one day to be able to have a child.
"I hope to touch people and in doing so to completely change the perception that the wider world has of this illness," she said of her documentary project. "We are invisible and people don't understand how severe and life-altering this is. If they knew it, we'd get the social support we need."