Stop mental fatigue: Science reveals why thinking drains you and how to fight back

Heavy decision-making, creativity or novelty appear to drain resources faster than repetitive or familiar work. (Picture Credit: Pexels)

For years, scientists treated mental fatigue as a vague concept. Now, thanks to advances in brain-imaging and metabolic studies, cognitive exhaustion is being examined with the same seriousness once reserved for muscle fatigue. Instead of viewing tiredness as a lack of focus or willpower, scientists are beginning to map it to real biological markers, shifts in neural chemistry, energy use, and activity patterns signalling that the brain is running low on fuel.

This new approach is opening up possibilities for understanding conditions like chronic fatigue syndrome, depression and long COVID, where people report lingering mental exhaustion long after their physical symptoms have eased. If the brain’s “engine” is struggling to keep up with demand, researchers argue, then therapies might be designed to support recovery rather than simply encouraging people to “power through.” And that, many say, could be a welcome shift from decades of dismissing exhaustion as mere mood or laziness.

Researchers notice that tasks that involve heavy decision-making, creativity or novelty appear to drain resources faster than repetitive or familiar work. It helps explain why a morning of intense problem-solving can leave a person feeling far more shattered than several hours of routine admin.

Here are signs your brain may be exhausted:

A sudden drop in motivation or interest

Difficulty making simple decisions

That foggy, slow-moving feeling behind the eyes

Trouble focusing on information you’d normally grasp easily

An urge to rest, not out of laziness, but necessity

Understanding the brain’s metabolic limits and chemical changes might help researchers develop therapies or better ways to manage prolonged cognitive fatigue. Researchers hope that, with better markers and clearer definitions, people will soon have real tools for managing cognitive load. And perhaps, in time, we might even learn to spot the signs before burnout takes hold.

FAQs on how overthinking drains you:

Because your brain stays in constant “analysis mode,” using up mental energy and increasing stress hormones.

Yes. It can cause headaches, muscle tension, poor sleep, and fatigue due to prolonged stress.

It creates confusion and self-doubt, making even simple decisions feel overwhelming.

It can—by causing misunderstandings, insecurity, and emotional distance due to constant worry.

Practicing mindfulness, setting boundaries on worry time, journalling, and focusing on problem-solving instead of rumination can help.