Many patients with severe health issues experience very normal depression - you'd be a bit abnormal if you didn't. But, depression isn't a symptom of any disease and both doctors and patients often mistake the symptoms of disease for depression.
Myalgic encephalomyelitis, sometimes called chronic fatigue syndrome, has nothing to do with laziness or motivation or burnout. All of those are curable - ME and CFS are not.
The IACFSME.org has a primer that you can print out to give your physician if they are unfamiliar with ME and CFS. The $15 donation is worth it to have accurate information that your doctor will find legitimate because it comes from researchers and clinicians who are experts in this disease.
As for determining whether you have ME and CFS here is the criteria commonly used by clinicians:
The 2003 Canadian Clinical Case Definition is summarized as follows and symptoms from all of the categories are required for a clinical diagnosis of CFS.
1. POST-EXERTIONAL EXHAUSTION: There is a loss of physical and mental stamina, rapid muscular and cognitive fatigability, post-exertional fatigue, malaise and/or pain, and a tendency for other symptoms to worsen. A pathologically slow recovery period (it takes more than 24 hours to recover). Symptoms exacerbated by stress of any kind. Patient must have a marked degree of new onset, unexplained, persistent, or recurrent physical and mental fatigue that substantially reduces activity level.
2. SLEEP DISORDER: Unrefreshing sleep or poor sleep quality; rhythm disturbance.
3. PAIN: Arthralgia and/or myalgia without clinical evidence of inflammatory responses of joint swelling or redness. Pain can be experienced in the muscles, joints, or neck and is sometimes migratory in nature. Often, there are significant headaches of new type, pattern, or severity. Neuropathic pain is also a common symptom
4. NEUROLOGICAL/COGNITIVE MANIFESTATIONS: Two or more of the following difficulties should be present: Confusion, impairment of concentration and short-term memory consolidation, difficulty with information processing, categorizing, and word retrieval, intermittent dyslexia, perceptual/sensory disturbances, disorientation, and ataxia. There may be overload phenomena: Informational, cognitive, and sensory overload -- e.g., photophobia and hypersensitivity to noise -- and/or emotional overload which may lead to relapses and/or anxiety.
5. AT LEAST ONE SYMPTOM OUT OF TWO OF THE FOLLOWING CATEGORIES:
A. AUTONOMIC MANIFESTATIONS: Orthostatic Intolerance: E.g., neurally mediated hypotension (NMH), postural orthostatic tachycardia syndrome (POTS), delayed postural hypotension, vertigo, light-headedness, extreme pallor, intestinal or bladder disturbances with or without irritable bowel syndrome (IBS) or bladder dysfunction, palpitations with or without cardiac arrhythmia, vasomotor instability, and respiratory irregularities.
B. NEUROENDOCRINE MANIFESTATIONS: Loss of thermostatic stability, heat/cold intolerance, anorexia or abnormal appetite, marked weight change, hypoglycemia, loss of adaptability and tolerance for stress, worsening of symptoms with stress and slow recovery, and emotional lability.
C. IMMUNE MANIFESTATIONS: Tender lymph nodes, sore throat, flu-like symptoms, general malaise, development of new allergies or changes in status of old ones, and hypersensitivity to medications and/or chemicals.
6. The illness persists for at least 6 months. It usually has an acute onset, but onset also may be gradual. Preliminary diagnosis may be possible earlier. The disturbances generally form symptom clusters that are often unique to a particular patient. The manifestations may fluctuate and change over time. Symptoms exacerbate with exertion or stress.
Carruthers BM, Jain AK, De Meirleir KL, Peterson DL, Klimas NG, Lerner AM, Bested AC, Flor-Henry P, Joshi P, Powles ACP, Sherkey JA, van de Sande MI. Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols. J CFS 2002;11(1):7 – 116
Many of these same authors were involved in the 2011 criteria as well.