Is both real and normal. I can't recall all the specifics, but it had to do with a number of psychological and physiological factors. Additionally, most people will undergo more than 1.

What to do about it? Learn everything you can. Do a lot of self analysis. Prioritize your life. Talk to people you trust and try not to do anything that can't be undone if needs be.

This is all stuff I learned as I dealt with my own mid life crisis. It was the toughest period of my life.