I think my friend is a pathological liar, HELP!?

i have been friends with this boy for a long time, ever since middle school, and we have been out of high school for a year now. he used to be normal, other than he got teased a lot because everyone called him gay in school and he had seflf-confidence issues with his weight. other than that, though, he seemed relatively normal. but, we had a falling out about a year ago and just recently became friends again and both my mother and i think he has, quite honestly, lost his mind. he tells weird, outlandish stories about his family, and then makes up reasons why we shouldn't ask them about it, and he has become extremely attention seeking and always wants to tell stories and wacky gossip that seems so ridiculous. but, the worst ever happened today. he has claimed he has been diagnosed with leukemia after they thought he had mono and none of it seems to line up. it seems like an insane attention ploy. what should i do? i think he is SERIOUSLY mentally ill. i want to go to his family, but i'm not sure how well that would go, because what if he truly does have it? he'd be hurt that i asked his family if he had it. what to do!?!? i just have a bad, scary feeling about this all! :/