I didn't know what to think of Chronic Fatigue Syndrome, but in the one specific instance of diagnosis I know of first hand, it preceded a diagnosis of terminal

I didn't know what to think of Chronic Fatigue Syndrome, but in the one specific instance of diagnosis I know of first hand, it preceded a diagnosis of terminal pancreatic cancer a bit later. Made me wonder if there could be a viral factor or something that leads to immune system problems that gradually develop over years.