I have never experienced medical school, so I have no clue what it's like, but it seems that the pressure is so intense that it causes some students to crack.
Could be. There is also the fact that certain mental illnesses develop in the early twenties - bi-polar, schizophrenia, etc. A friend's daughter had just graduated university when she began exhibiting odd behaviors and physical manifestations of a rare disorder. She lived in a group home and died of choking a couple of years ago at age 30.