A history, from Scientific American:
[Season’s of a Man’s Life author] Levinson felt that midlife crises were actually more common than not and appeared like clockwork between the ages of 40 to 45. For Levinson, such crises were characterized primarily by a stark, painful “de-illusionment” process stemming from the individual’s unavoidable comparison between his youthful dreams and his sobering present reality. For most men, life moves so swiftly that, by the time you look back at what’s happened, you realize you’ve already suffered an irreparable loss of chance and opportunity. This life review causes depression, anxiety, and “manic flight,” a sort of desperate, now-or-never fumbling to experience the pleasures one has long denied oneself and an escape from stagnation.
(via MindHacks)