i have younger identical twin sisters (50 years old). One of them seems to be a chronic liar and a hypochondriac. She lies to make herself look better, to get out of doing things, and lies about herself by saying things have happened to her that actually happened to other family members. She works at the same place as her twin sister and lies to take credit for her work. When asked what she did over the summer she lied and said she did something that I had done. Our older sister was just diagnosed with ovarian cancer and she immediately ran to the ER with the same symptoms to get completely checked then led people to believe she has cancer. Her twin sister had an ovarian cyst and she told people at work she had the cyst. She has been complaining of illnesses for years and running to the ER with nothing ever wrong with her. Our parents are very old and no one in the family wants a confrontation so no one calls her on her on her lying. Up until now most have believed her except her twin sister because she has grown up close to her. They don't get along well and are competitive. Why does my sister lie constantly ? It's become worse since the cancer diagnosis of out other sister. The lies are easily proved but she doesn't seem to care. Is it because no one has ever help her accountable she thinks we are too clueless to know? Is this a mental illness? Thanks for any advice.