Daniel Hodgson, 38, requires round-the-clock care from his family and cannot stand up for longer than five minutes without enduring debilitating head pain which can last for several days.
The father-of-two, who lives in Richmond and runs his own wall art company, underwent tests at six different hospitals after he collapsed and NHS doctors initially suspected he had contracted viral meningitis, but they were unable to provide him with a diagnosis or effective treatment.
The family claim he also suffered from a spinal fluid leak after a doctor made an error when performing a lumbar puncture.
They decided to take him for private medical care at BMI The Alexandra Hospital in Greater Manchester, where the medical staff performed a procedure to treat the spinal fluid leak and provided him with a long-awaited diagnosis.
Doctors concluded that a viral infection has damaged Daniel's brain and nerves, and they are now trying to draw up an effective treatment plan, but his family can no longer afford to pay the medical bills.
His sister Jema Barton, who said the family are at "breaking point", has set up a GoFundMe page to fund the treatment and well wishers have donated more than £2,200 so far.
"Every single day, he's getting worse," she said. "The more he lays still and is unable to move, the more his body just shuts down on him.
"Two weeks ago he was able to move his arms and his leg, but now when he's sat on the bed he struggles to even lift a cup because he's got no strength left in his arms.
"He's got spasms going on in his neck, through his nerves and that's going through his arms and legs. Each week it's spreading to another part of his body - it's horrible."
She added: "I just want my brother back, talking to him now he doesn't sound like my brother anymore.
"If everyone who reads this donates...that will make such a big difference."
You can make a donation by visiting the GoFundMe page.