In my case, too much thought or mental activity will exhaust my mind, and leave me unfit for any further mental tasks. In this exhausted state, I become a bit zombified, and this tends to make me sit around with my brain in neutral, doing nothing.
The above describes my experience.
I am not depressed. But I have very little motivation. It's mainly because I can't do much "big stuff", that I don't desire to do much. I have a constant mental and physical fatigue. My head is on 20% power. I'd rather close my eyes and rest my thoughts (not rest my feelings, though). This is so unlike me - my brain was always the most active and alive part of me!
I do not have the motivation to plan anything big, or even anything small, because I won't be able to do it, energy-wise. I have watched many of my prior life plans fall through, and perhaps become permanently unavailable to me. I am not angry at that, I am sad about it, and trying to accept what I ought to for my own peace of mind, and trying to work out what is still possible, as the birthdays tick by. I am not depressed.
Some people might conjecture that I have mental depression, looking at my symptoms/feelings (if they don't look at the rest of my physical health problems), but it's a slightly different thing. My underlying spirit and thoughts and moods are not depressed at all.
I do not have, nor have I sought, a medical diagnosis of CFS/ME (although I've had life-changing fatigue and related symptoms for several years), so I don't feel that my opinion is equal to the opinions of you who have been deep in the trenches for years with CFS/ME. I am not jumping into the argument because I could not be a full-fledged participant.
I don't know much about CFS/ME, but I know that anything that has a whiff of psychology is a touchy subject for people who have been misunderstood and misdiagnosed by so many medical professionals, and who may bristle at anything that sounds like they are being told they have a "mental" problem. I'm not saying what anyone has is even remotely a "mental" problem.
...Not that there is anything wrong or "lesser" about having a mental health problem, which is often at basis a "real" physical problem anyway, if the investigation is good enough.
(Even the condition of being a sociopath shows a discernible pattern on brain scans for most sufferers.
http://www.scientificamerican.com/article.cfm?id=can-you-make-sociopath-through-brain-injury-trauma
http://www.technologyreview.com/news/407738/what-can-neuroscience-tell-us-about-evil/
http://www.npr.org/templates/story/story.php?storyId=128116806)
Maybe different folks define "motivation" differently. I have no problem saying that I have very little motivation. I don't feel bad about that. Why couldn't lack of motivation be felt concurrently with a host of other symptoms? How is it different from having frequent headaches or having slow-moving bowels or poor blood circulation in the extremities?
"Motivation is defined as the process that initiates, guides and maintains goal-oriented behaviors. Motivation is what causes us to act, whether it is getting a glass of water to reduce thirst or reading a book to gain knowledge.
It involves the biological, emotional, social and cognitive forces that activate behavior."
http://psychology.about.com/od/mindex/g/motivation-definition.htm
"Fatigue is different from
drowsiness. In general, drowsiness is feeling the need to sleep.
Fatigue is a lack of energy and motivation.
Drowsiness and apathy (a feeling of not caring about what happens) can be symptoms that go along with fatigue."
http://www.nlm.nih.gov/medlineplus/ency/article/003088.htm
I have fatigue -- I have "a lack of energy and motivation".
I am not apathetic, however. I am not down on myself. I am cheerful and calm.
I have until recently been iron deficient. I have the compound heterozygous MTHFR mutations and worsening symptoms of folate and B12 deficiencies, including vision damage at a relatively young age. I have had an underactive thyroid for years. I have low DHEA-s. I am deficient in Vitamin D. I may have cancer. I may have adrenal gland hypofunction or whatever it's called. I may have some pesky viruses - I was thought in my 20s by my doctor to have Lyme when I was living in one of the hotspots for it, but the blood tests never came back positive; then I came down with shingles in my 30s. I may have macrocytosis (depending on whose scale is used; Wikipedia thinks I do). I have had delayed sleep phase disorder all my life. So, yes, I have fatigue. And now, in the last few years, I have no motivation. I feel absolutely blase about everything. I have been in a holding pattern for a number of years and I simply cannot force myself through willpower alone to do things -- that ability was burned out. I also have had since I was pretty young an anomie and existential despair which is nothing to do with typical mental depression, more just a spiritual position. Since I have several physical problems that can be pinpointed and can be treated, I would not look for a CFS/ME diagnosis, and I am just really glad to finally know (through blood tests that I ordered for myself, after being told by doctors for years that nothing was wrong with me and nothing could be found) that I've got a number of these physical problems that I can work on to try to improve my health and lessen my fatigue.
People here (who officially have
Chronic Fatigue Syndrome/ME) seem to have so many different constellations of symptoms. Why can't a lack of motivation be a possible symptom amongst the hundreds,
if the very definition of fatigue is a lack of energy and motivation? I am sure that there are layers to this that I cannot possibly know. I'm just explaining my view.