Many physical and mental health problems are stress related. The mind control you are unconsciously put through as a dub is unrelenting, and enough to trigger any number of health problems - for some this shows itself mentally, for others physically. I know several who would fit this category.
Take this example : Sister Chronic Health Problems has served faithfully for decades as a pioneer, never been able to marry, always had strong opposition from her non-JW family which has caused her constant turmoil and stress all these years. Add to this that she dropped her education when she learnt the truth and decided to pioneer and so has always struggled big time to make ends meet and have adequate accommodation. Nearing retirement and still on a job most people only do for a couple years when they're young, for the past few years her doctor has signed her off work half the time as she can't take the stress levels there. This has resulted in constant physical and health problems which costs alot especially for someone on a part-time minimal wage. All this because she decided to give her life to a publishing company. (Her brothers and sisters don't have these problems.)
Add to this, when you have chronic health problems in the borg, the number of times you are referred to some magic doctor (often some witness who has to be ok as even the Bethel sends people to him or her) who turns out to be an absolute quack, but you go to see anyway as Brother Insistant is convinced Dr Magic is sure to be able to cure you as he did for Brother Supposedly No Longer Sick, and you don't want Brother Y to think you're spir'ly weak as if you get better, then you'll be able to go to meetings again. Oh, and ultimately, these are all doctors that are not covered or recognised by any social security, and so you have to pay out of your pocket. And when you call Brother Supposedly No Longer Sick to check out about Dr Magic, you find out that actually, he didn't get any better. It happens time and time again and is not unique to one part of the world.
Poor Sister Chronic Health Problems went to see several of these doctors and they never had more than a placebo effect on her. Some of the things these doctors say or use as techniques or treatments are completely...well you know.
And to finish, what about those who gave their best to the borg and suffer now from burnout?