That is very true, Kiwi. The first example, someone who is injured, and will take a long time to heal is one case. The other, someone who can never do "their" sport again, is a different problem. There are therapists who specialize in sports psychology, and they deal with stuff like this. There's a grieving process involved, especially in the second case, and it's a major life transition, so all of the issues that would be involved with that are present.
I've experienced the first, and I always looked at an enforced "break" from riding, or at earlier point in my life, from teaching fitness classes, as the time to learn something new, that met the same need. While I may not have liked it at first, I generally focused on that, and healing, so I could eventually get back to riding.
AZ, I love your husband's story. Sleep issues affect so many people, and I really didn't realize this until I did my first internship.