Why Is Thinking Too Much so Tiring?

Thinking too much can cause you to experience fatigue and exhaustion. We'll review some of their motives according to the scientists.
Why Is Thinking Too Much so Tiring?
Laura Ruiz Mitjana

Reviewed and approved by la psicóloga Laura Ruiz Mitjana.

Last update: 25 February, 2023

Have you experienced tiredness from thinking too much? You’re not alone. In fact, this is a very common problem, one that affects millions of workers around the world. You come home from work and even though you haven’t been physically active, all of a sudden, your strength and energy seem like they just drained over the course of the day.

Simple activities like doing chores, walking the dog, exercising, and even going out with your friends or family seem like daunting tasks. There are many explanations for why thinking too much causes burnout. Today, we’ll evaluate two possible catalysts and teach you how to recognize the initial state to avoid mental fatigue.

Glutamate is possibly responsible for tiredness from thinking too much

A study published by a group of French researchers in Current Biology in August 2022 could give clues about fatigue from thinking too much.

The scientists evaluated the chemical composition of the brains of two groups of people over the course of a workday. One of the two groups was assigned more demanding and complex cognitive tasks, all with the aim of analyzing the impact that these had on a physiological level.

The experts found that fatigue, reduced performance, and reduced pupil dilation occurred only in the group that performed the most complex activities. Through an analysis of magnetic resonance spectroscopy, they discovered that work with a high  cognitive demand leads to an accumulation of glutamate in the lateral prefrontal cortex.

Glutamate is the main neurotransmitter of the central nervous system. Similarly, it’s the most abundant neurotransmitter in the brain. Among many other things, it mediates the regulation of excitatory brain activity.

In addition to this, and considering its wide abundance in the body, it has been suggested that it has a leading role in communication, learning, and neuronal regulation. We know that its excess can cause excitotoxicity and neurodegeneration.

Returning to the research of the French scientists, they warn that, at least until now, it was thought that mental fatigue was a kind of illusion generated by the brain to make people abandon a complex activity that was being carried out.

This work consolidates a precedent that complex cognitive activities, such as thinking hard, lead to a real physiological alteration with physical and psychological implications.

Stress, another cause of tiredness from thinking too much

Tiredness from thinking a lot due to stress.
There are several mechanisms through which stress induces fatigue when thinking too much.

Demanding cognitive tasks often lead to stress. This is a very complex process that’s triggered in the body to deal with a problem.

It’s mediated by many hormones, among which cortisol is one of the most important. Specialists use the term stress-related burnout disorder to refer to tiredness, fatigue, and exhaustion triggered by prolonged episodes of stress.

Work published in NeuroImage: Clinical in 2020 found that mental fatigue is a central component of the clinical manifestations of stress-related burnout disorder.

Difficulty concentrating, decreased alertness, disordered thoughts, lethargy, reduced work efficiency, and a propensity for errors are some of its consequences.

This symptom adds to other classic stress symptoms, such as muscle aches, headaches, shortness of breath, chest pressure, blurred vision, sleeping problems, and gastrointestinal problems.

All of this adds up to the perfect cocktail for developing fatigue from overthinking. The fatigue you then experience may be a consequence of the stress of the cognitive task.

How to recognize mental exhaustion

A woman driving while experiencing mental exhaustion.
It’s important to detect the symptoms of mental fatigue early on. These appear progressively, and, in the end, they’re very bothersome.

Now that you know why thinking too much causes fatigue, you should also know that there are ways to prevent you from reaching this state. Typically, this type of tiredness appears only after the appearance of a series of well-defined signs or symptoms. We’ll leave you with some of the most important:

  • Feelings of impatience
  • Irritability and sudden mood swings
  • Drowsiness
  • Excessive anxiety or worry
  • Changes in eating habits (with a predisposition to sugary, salty, or fatty foods)
  • Lack of motivation
  • Feelings of hopelessness

As expected, all of these manifest gradually, so by identifying them, you can put a stop to their snowball effect. Many times, when you’re focused on a problem or an idea, you overlook all these signs. Now that you know what they are, you can take the necessary steps to prevent intrusive thoughts from completely dominating your day-to-day life.

  • Gavelin HM, Neely AS, Dunås T, Eskilsson T, Järvholm LS, Boraxbekk CJ. Mental fatigue in stress-related exhaustion disorder: Structural brain correlates, clinical characteristics and relations with cognitive functioning. Neuroimage Clin. 2020;27:102337.
  • Grossi G, Perski A, Osika W, Savic I. Stress-related exhaustion disorder–clinical manifestation of burnout? A review of assessment methods, sleep impairments, cognitive disturbances, and neuro-biological and physiological changes in clinical burnout. Scand J Psychol. 2015 Dec;56(6):626-36.
  • Hertz L. Glutamate, a neurotransmitter–and so much more. A synopsis of Wierzba III. Neurochem Int. 2006 May-Jun;48(6-7):416-25.
  • Stallard, C. N., Anoruo, M., & Saadabadi, A. Biochemistry, Glutamate. In StatPearls [Internet]. StatPearls Publishing. 2021.
  • Wiehler, A., Branzoli, F., Adanyeguh, I., Mochel, F., & Pessiglione, M. A neuro-metabolic account of why daylong cognitive work alters the control of economic decisions. Current Biology. 2020.

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