Bobby Parnell raised his right arm to just above his waist. He was showing The Post how badly the pain affected him before he underwent neck surgery last Sept. 10 to repair a herniated disk. “The pain was bad,’’ Parnell said. “Real bad.’’ The good news for the Mets is the pain is gone and Parnell now has full movement of his arm, and the closer sees himself on the fast track to recovery. “I feel great,’’ Parnell, 29, said Monday as 49 Mets from all different levels of the organization gathered for pre-camp workouts. Manager Terry Collins surveyed the scene and said: “Bobby is going to be huge for us this year.’’ All the closer talk in New York has been about David Robertson taking over for Mariano Rivera, but the fate of the Mets rests on Parnell’s right arm. If Parnell can’t come back from his surgery, the Mets will once again have too many holes to fill before the season even gets underway. Parnell is one of the most well-liked players in the clubhouse, and the starting pitchers are counting heavily on Parnell being 100 percent by the time the season starts. The hard-throwing right-hander converted 22 of 26 save opportunities before his season ended early, and in two of those blown saves, it was the defense that cost the Mets, not Parnell’s pitching.