My husband and I were talking with some friends of ours. Our friend had come back from a long day at his residency, working at an emergency room at a local hospital. He was on his first year of residency. He looked tired and worn down. So did his wife. I don't remember exactly how we got on to the topic, but I had asked him why he wanted to be a doctor (I'm always interested in people's motivations for why they do what they do). I don't remember his answer because it was overshadowed by what he and his wife followed with afterwards: "I wouldn't do it again." I understand that the life of a med student and medical resident is hard. Long hours at school and work and many years of dedication. But it still saddened me that he would say that.
If you are doing what you really want to do, what you feel you should be doing, if you had to do it all over again why wouldn't you? I feel that if you have really found your passion that no matter what circumstance arises if you have to start over, or if you find yourself in another life you'll always find yourself going back to what you were doing before. No matter what, no matter how hard if it's your true calling, your real passion you would always do it again.
And if you find yourself saying "No, I wouldn't do it again," then why are you still? I understand that in the regards of med school a lot of money and time has been invested and there may be some guilt associated with quitting something that you have already put so much in to, but to live a life doing something you would never do again given the chance doesn't seem worth it to me.
I hope that you don't find yourself in this situation. I hope that when asked if you would do it again you would say with whole heart "Yes, I would." I hope that everyone has the opportunity to be anxiously and vigorously engaged in a trade/skill/job/career that they love and enjoy.