Sheesh, I don't know. Med school is 4 years of your life. A lot of people, when subjected to any random four year stretch of their life, particularly the years after college, are going to get depressed and feel burned out, particularly when friends from college are in the work force and moving on with their lives. When you're in med school you still are a student, and you also realize that it isn't really going to change much until you finish residency (other than getting paid a little bit instead of paying a lot).
I think a lot of it is overblown. Med students have a lot of stresses but if you look at any group of people you'll probably find similar statistics about burnout and stress and regretting your career path and even suicidal thoughts. I do think, though, that there are more and more people entering med school who are just doing it because that's what they're supposed to do, and not because they have really considered other things or know what they want to do with their lives. Burnout is going to happen when you start realizing that the course you have set yourself on is somewhat permanent - you can't really change your mind anymore because of your loans and all the time you invested.
I enjoyed years 1-2. Year 3 was hard but I knew it was only a year. I got sort of burned out year 4, not from being busy or stressed but because I felt like I was just wasting time for a year until I started residency.