There are many ways to develop energy failure and mind failure. Running low on glucose for example [hypoglycemia]. Or running low on insulin [Diabetes] so you cannot utilize glucose. Or running low on water [dehydration] or running low on thiamine, iron, or other nutrients [malnutrition]. Or running low on blood [blood loss] or running low on body heat [hypothermia] or running low on calories [weight loss] or running low on muscle [muscle wasting] etc…..you get the idea.
Any kind of energy failure will affect the mind, in different ways, none of them good. Any kind of energy failure [oh energy failure can also occur from damage to organs – heart failure, kidney failure, skin failure – did you know that some conditions cause all your skin to suddenly fall off -ouch! – liver failure, respiratory failure, etc…
Energy failure from any cause will be difficult to detect, because the body is organized with lots of redundancy, allowing you to remain alive and ambulatory for a long long time before anyone suspects energy failure.
Mind failure is kind of the same, it is visible [in the deterioration of your mood, thoughts, behaviour and amount of activity] -but your behaviour will adapt slowly to the level of energy remaining, without you becoming aware of it.
It may not even become obvious what is causing the mind or energy failure until an autopsy is done.
And some forms of energy failure are dynamic and part of being alive, so there may be few clues as to the cause of the energy failure.
For example, gradual asphyxiation [from any cause-external or internal] is not easily visible on autopsy. Asphyxiation only leaves nonspecific signs in death. It is hard to see. https://www.tasanet.com/Knowledge-Center/Articles/ArtMID/477/ArticleID/338920/Forensic-Analysis-of-Injury-and-Death-by-Asphyxiation
The normal function of mind is reversibly dependant on the availability of excess energy. One can remain alive without the function of their mind; it would be a miserable existence, true, but it is possible.
And that is how Paula felt during her episode of mind failure – miserable. Everyone knew something was terribly wrong with Paula but no one knew about her mind failing and of course she couldn’t tell them because her mind was not working well enough for her to say.
She had enough energy to stand and to sit, but not enough to stand or sit straight. We forget that posture takes work on the part of the muscles and the nerves and the brain. She could only slump. So people knew something was wrong with Paula all right; it was visibly obvious. And so nonspecific. You just couldn’t quite put your finger on it……unless you thought to check the silent function of the complex motor act of breathing at rest….
Of Sound Mind 