I am also a fitness instructor who teaches about 15 classes a week. In the last few years I noticed a few symptoms of overtraining. So I took up yoga and teach it restorative-style, studied up on elder fitness and teach several a week, started some bootcamps where I am more of a coach than participant, and added circuit classes. I teach a couple of strength classes and participate to get my "lifting heavy stuff " in and teach a low impact cardio class. I do not work weekends so I try to get a good low and slow hike in at that point. This is working for me. Combined with the elimination of grains (for the most part) I know longer feel the pain of overtraining.
I have already retired from my "real " job (at 47!) And now get to do what I love. I don't plan on retiring again anytime soon, but if and when I do I will have lots of long hikes, yoga, and lifting still on my agenda. I am 52 and have never felt better. I eliminated wheat in. Jan. 2012 and am working on the paleo aspect for the last month or so.
Good luck on your journey fellow instructor!