I hurt my back and neck doing Cross Fit years ago.
At that time I also came down with chronic fatigue, so nothing seemed to heal right.
The only exercise I've been able to do since then is Yoga.
If I did even 10 pushups, my neck would hurt for weeks.
If I tried to lift weights or do calisthenics, I'd throw my back out, and it'd last for 1-2 months!
I was really starting to get depressed every time it happened. It seemed like I was always in pain.
I actually started taking this, because I heard it was good for stress (which it totally is!).
But then I noticed my pain starting to go away. At first, I didn't even know what was doing it.
Now, I'm lifting weights again, and doing exercises I only dreamed of a few months ago.