Serotonin the new 'Cure All'

[Leopardtail]

• Difficulty concentrating, remembering details, and making decisions
• Fatigue and decreased energy
• Feelings of guilt, worthlessness, and/or helplessness
• Feelings of hopelessness and/or pessimism
• Insomnia, early-morning wakefulness, or excessive sleeping
• Irritability, restlessness
• Loss of interest in activities or hobbies once pleasurable, including sex
• Overeating or appetite loss
• Persistent aches or pains, headaches, cramps, or digestive problems that do not ease even with treatment
• Persistent sad, anxious, or "empty" feelings
• Thoughts of suicide, suicide attempts

These are some of the official symptoms of depression and most of the CFS patients do have these

My experience of ME patients is not "lack of interest" in hobbies etc but lack of energy to participate in them and profound frustration about. That contrasts with depression where the issue is genuine lack of interest. The "decreased energy" seen in depression is increasingly seen to really be lack of motivation in that once a person with clinical depression gets active, they are capable of exercise and benefit from it, where we get worse. Many specialists in ME recognise that their patients show remarkably little depression for people in their circumstances.
Personally I have periods of good mood and high motivation in which I still lack the fundamental energy to do stuff. It's also important to realise that many 'symptoms' of depression would only occur with awful levels of Serotonin that would have dominantly psychological symptoms. It's also important to understand that many people diagnosed with depression wrongly have serious hormonal issues causing the problem and are not in fact suffering clinical depression but situational depression (the two are different).