Understanding the Mid-Life Crisis by Peter O'Connor is out of print but sometimes found in library or Amazon. Doesn't kill you with technical but goes deeper than the feel good books.
If you want to step over to the other side and read something the IC might suggest to someone in crisis, "In The Meantime" by Vanzant. It views the world as a multistory house with a basement. All our trash is in the basement that we must get in order before we can go to the next level. We have more work to do there before we can go upstairs to the peaceful room with a view. There is different work to be done there. It is uncomfortable to read the parts that tell you to just throw it all away and go for the passions you desire - as you begin cleaning the trash out of the basement. I didn't like thinking I was trash.
But the rest of the book could be for all of us dealing with dramatic change in our life. We all have to clean our own basements and work our way back up to the comfort of our room with a view.
I am sure others here can list a great number of books. I've seen many mentioned here but can only handle so many words in one lifetime.
