The disease itself causes the neuropeptide levels in the brain to decrease, affecting a Vulcan's ability to maintain logical control. Fal-tor-voh requires a mind meld with a compatible patient, which usually means a blood relative.
Tuvok suffered from the disease in 2378 which required him to take treatment as he was beginning to show signs of a lack of control and displays of emotion. However, he was on board the USS Voyager and trapped in the Delta Quadrant and as none of the Vulcans on the ship were compatible, he was required to reach the Alpha Quadrant in order to find a relative that could perform the fal-tor-voh treatment. (VOY episode: "Endgame")
Upon their arrival at Earth, Tuvok's son Sek was one of the first people allowed on board Voyager so that he could immediately see to Tuvok's needs. Tuvok was cured of the disease after a successful mind meld with Sek. (VOY novel: Homecoming)