Image by bluman via Flickr
I know many CFS patients suffer muscle and joint pain, especially after they wake up in the morning. I used to suffer the same symptom many times in my life but each time the pain did NOT last very long, because I found the reason: my bed was too "thin".
As seasons change I change my bed set. Almost inevitably every time when I got body and joint pain I would find that my bed was not thick enough to resist something bad for my body: cold air in winter, humidity in spring or summer. And soon after putting extra pads on the top of my bed, the symptom went away.
In China, it was a common sense that during winter, people need to put extra pads (or blankets or quilts) on the top of bed. Here is the reason (I am not a doctor nor a scientist so forgive me for not explaining this like an expert, but I try my best to make sense based on my own experience): when our body gets weak, out immune system would be too shaky to resist coldness, humidity, virus, etc., especially when our body is in rest. So when we sleep, we must protect our body in a nice and warm environment. Putting blankets on top of our body is just one side protection, the bottom side (top of mattress) should be also protected. If not, you may still feel "fine" but your body would struggle on fighting with those cold air or humidity, and exhausted when you wake up in the morning.
Of course, there are many other causes for body pain but, if your bed is thin (just a mattress and sheet), please just do an simple experiment by putting extra blankets (or pads or whatever other thing you have), and see what happen in next morning.
For back pain, soft mattress usually is the cause, but I guess this is already a common sense in this country.