My father had a hernia repair surgery after proper testing. He was having frequent back ache and pain in the abdoman due to which he went to a doctor. The doctor diagnosed it as hernia. I guess in the case of people who gets an undiagnosed hernia removed it may have been in the beginning stage and so the patients may not have recognised the symptoms. Otherwise hernia can be detected through proper tests and we need to undergo a hernia surgery for its removal.