My own view on why a host of "vague" physical diseases seems to afflict the JWs is very simple and avoids mumbo-jumbo about psycho-dynamic processes :
Having a physical disability is about the only "legitimate" way to get out of the rat race of boring witness activities. If your physician diagnoses one of the "newer" physical disabilties, you virtually have a ticket to greater freedom from endless activity.
Even physically healthy inactive JWs often live in dread of being pressured to do more. At least if you have Chronic Fatigue Syndrome you can convince your local congregation to give you a break. I suppose having a physical disability is the body's own way of protesting against the boring witness treadmill!