That happened to me, but then I convinced myself that I can do better and boom I created better as in nearly doubled my salary and was as happy as I ever was...then that became the new bar. Frustrating cycle, but it will come back around.
Funny...as I age I tend to have a similar view. But we're told hindsight is 20/20. The one motivating factor for me is the fact that a lot of what I have accomplished has made a difference to those who have shared in it. Which, to me, means we're doing incredible things people envy just at a different scale. Besides..there may not be a tomorrow, but there is always a today to do something better.