My experience as a CFS patient was that I had a very depressed period of about 5 months were I slept 16-18 hours/day. Then I recovered somewhat to where I was able to do day to day activities and only needed extra sleep when I did more than normal activities. Am I correct that in the model discussed in the paper this would conform to being in a very depressed steady state, then moving to a less depressed steady state. If this is to explain CFS how do you explain this transition between two apparent steady states without intervention? Perhaps the highly depressed state is less stable than the moderately depressed state and my body was able to make that transition on its own. Your model also assumes that all these chemical systems are functioning normally, but there is also the possibility of a problem in some part of the control mechanism.