A change in the companies managing health care for more than 118,000 people sickened by the Sept. 11, 2001, attacks has proven a nightmare for many enrolled in the program. Obtaining medicine and getting other treatment is difficult for people like ex-volunteer firefighter and Marine veteran Dan Moynihan, who spent a month working at ground zero. Toxins from the rubble and the surrounding area gave Moynihan recurrent cluster headaches that are sometimes called “suicide” headaches because they’re extremely painful and can land their sufferers in the hospital. Moynihan’s doctor has prescribed hi…