You answered a few emails, ran an errand or two, checked your phone more times than you’d like to admit and somehow, by evening, you’re running on empty. No crisis. No deadline disaster. Just tired.

According to researchers who study mental fatigue, that feeling is real, and it’s rarely caused by one dramatic event. Instead, it tends to build gradually, through a long list of small decisions, interruptions and habits that quietly chip away at focus over the course of a day. On their own, none of them seem like much. Added together, they can leave the brain running on fumes.

Here are 10 everyday habits researchers say may be draining your mental energy without you realizing it.

1. Making thousands of tiny decisions

Behavioral science reviews estimate that adults make roughly 35,000 decisions a day, from what to eat to which text to answer first. Psychiatrists who study self control say each of those choices pulls from a limited mental reserve, which can leave the brain feeling tapped out by nighttime, sometimes resulting in impulsive snacking or irritability that seems out of proportion to the day.

2. Refusing to commit to a plan

Keeping every option open might feel low key, but researchers have found that self control erodes faster as the number of choices piles up, particularly when the tradeoffs aren’t clear. Leaving meals, plans or purchases unresolved keeps the brain stuck comparing possibilities long after a decision was actually needed.

3. Scrolling in every spare moment

A study published in the journal ScienceDirect found that the information overload and social demands of heavy social media use can raise both fatigue and anxiety. Scrolling requires the brain to process updates, read social cues and manage emotional reactions, all of which can leave people feeling mentally worn out even after time spent supposedly relaxing.

4. Keeping the phone within eyesight

Research from the University of Texas at Austin, published in the Journal of the Association for Consumer Research, found that simply having a smartphone nearby, even powered off, can reduce working memory and lower measures of fluid intelligence. The effect was strongest among people most attached to their devices, since extra energy goes toward resisting the urge to check them.

5. Sitting still for hours at a time

Reviews in the National Library of Medicine link long stretches of sedentary behavior to weaker cognitive performance and a higher long term risk of decline. The fix doesn’t require a full workout. Studies show that breaking up sitting with brief movement can improve attention and memory almost immediately.

6. Relying on ultra-processed food

A 2025 study in the journal Nutrients found that people who got more than about 40% of their daily calories from ultra-processed foods reported higher mental distress and lower overall quality of life. Researchers say these foods tend to be high in calories but low in the nutrients that support healthy brain function.

7. Scrolling in bed to wind down

Harvard Medical School research has shown that blue light from phones suppresses melatonin and delays the onset of sleep, disrupting the body’s natural circadian rhythm. That can lead to fragmented sleep, meaning someone can log a full eight hours and still wake up mentally foggy.

8. Multitasking through the day

Research from the American Psychological Association shows that nearby devices alone can pull at attention, and switching between tasks makes it worse. Every time the brain reorients to a new task, it burns through mental energy faster than it would completing one thing at a time.

9. Skipping breaks during desk work

Randomized trials in occupational health journals show that short, regular movement breaks meaningfully improve working memory and problem solving. Skipping them tends to leave people more drained by day’s end, even when the work itself wasn’t physically demanding.

10. Assuming mental energy is unlimited

Psychologists describe decision fatigue as a natural response to sustained mental and emotional load, not a character flaw. Pushing through without recovery time can lead to procrastination, self criticism and irritability, further depleting the reserves people are trying to draw on.

The bottom line

None of these habits look dramatic in isolation. Together, they explain why so many days that seem easy on paper end in real exhaustion. Experts say the goal isn’t to eliminate every distraction, but to recognize that the brain, like the body, has limits and needs real recovery to keep functioning well.