For nearly 40 years, Sharon Pikus hid what she calls her “dirty little secret”: After an adolescent case of whooping cough caused her to vomit everything she ate, she turned the experience into a trick to lose weight. “I was always a chubbette as a kid, so I said to myself, ‘This is terrific — I can eat whatever I want and throw it up,’ ” recalled Pikus, now 60. She kept up the habit for decades, eventually having to hide it from her husband and children. Even as other parts of her life were in place — her family was happy, her business was successful — her bulimia lurked under the surface, an overwhelming compulsion.