The stress response is a get-ready system. It speeds the heart, tightens muscles and sharpens attention so you can act, and it is meant to fade once the moment passes.

It does not need a physical threat, and in a laboratory study of 62 women, mental arithmetic and a word-and-colour test alone raised muscle activity in the shoulders.

Most of this runs below conscious awareness, so you notice the result, the jiggling foot or the urge to get up, rather than the signal that started it.

Researchers treat this as a core part of stress. A widely used stress scale is built around finding it hard to wind down, sitting beside feeling on edge and easily upset.

Switching off is the weak link: in one experiment, blood pressure stayed raised longer after an upsetting task than after hard exercise that pushed it up just as much.

Holding the stress in mind is what keeps it there. People given a small distracting task after the stressor recovered better than people who sat quietly and stewed.

Trying hard to relax can backfire too, because people told to relax while under mental load showed more signs of arousal on their skin, not fewer.

So the loop feeds itself. Restlessness is not a lack of willpower, it is a system that has not yet had a clear signal that it is safe to stand down.

Restlessness comes from the part of the nervous system that prepares you for action. It raises your heart rate, tightens muscles and pushes attention outward, which is useful when there is something physical to do, like lifting, running or reacting quickly.

It is built for short bursts: you meet the challenge, the body uses the energy, and a calming branch of the same system brings everything back down again, usually within a few minutes of the demand disappearing.

Modern pressure rarely works like that. A tense email or a money worry calls up the same readiness, but there is nothing to run from or push against, so the energy leaks out as fidgeting and pacing.

This is common: in a 2018 federal health survey, about one in five US adults said they had felt restless at least some of the time in the past month. Stress scales used by researchers list trouble winding down as a core sign.

The trigger is a judgement the brain makes about what is at stake. There are two routes out: fast nerve signals that act within seconds, and slower hormones that keep the body ready for longer.

A purely mental task is enough to start both. In a lab study of 62 women, mental arithmetic and a word-and-colour test raised shoulder muscle activity, with no lifting or physical work at all.

Stress also shows up in small movements, and during a public-speaking test, 42 healthy men who felt more anxious going in scratched, touched their face and bit their lips more often, even though nobody had told them anything about their movements.

The men who fidgeted most reported feeling less stressed afterwards, although a follow-up found this in men but not in women. Fidgeting may be the body letting off steam, not a fault to fight.

You do not need a crisis to feel this. The same restless state turns up after an ordinary busy day, and people often dismiss it because nothing dramatic happened. Small, steady demands add up across a week in a way that single events rarely do.

The amount of pressure matters. In a diary study of 87 workers, a heavier workload during the day predicted a harder time switching off mentally that same evening, and switching off was in turn linked with better mood and less tiredness at bedtime.

The pattern holds at scale, too. Pooling 91 samples and 38,124 employees, higher job demands went with less switching off after work. The link was small, but it held across very different jobs.

Teachers show the timing clearly, since those under high strain were still thinking about work at 8 and 9pm, when colleagues under lower strain had mostly let go. That was a small study of 69 teachers, so hold it loosely.

Stress is rarely the only input, and caffeine is a common one. In a small trial of 12 adults, a 500 mg dose brought more restlessness, tension and nervousness than a 250 mg dose did.

Short sleep matters too, because after a night without sleep, healthy adults in a lab study felt clearly more anxious the next day, and even small nightly losses tracked with more anxiety, which means a rough night can make an ordinary stressful day feel far harder to shake off.

Some medicines can cause an inner restlessness, especially when the dose of certain antidepressants goes up. Hormones count as well. In a 10-year study of 2,956 women, those who were calm before menopause often grew more anxious during it.

Hours of sitting still with a phone lighting up give the body readiness with no outlet. A strong urge to move your legs at night, or fidgeting you have had since childhood, is worth raising with a doctor instead.

Repeated often enough, staying on alert becomes the default. The body starts to expect the next demand, and evenings feel like a pause between tasks rather than real rest. Checking messages late in the evening keeps that expectation alive.

The good news is that recovery can be trained. In a study of 95 workers, two short sessions on switching off and relaxing improved recovery and sleep, and lowered stress, three weeks later. It did not change exhaustion, which suggests deeper burnout needs more than a short course.

Relaxation methods help on average: across 27 studies, relaxation training gave a medium drop in anxiety, and slow breathing practice lowered stress across 12 trials with 785 adults.

Movement helps in the moment, and a single bout of exercise gave a small but real drop in anxious tension across 36 trials, which fits the body’s wish to use the energy it has raised.

One common belief is wrong: that you stay wound up for hours because adrenaline is still in your blood. It clears within minutes. What lingers is the mind replaying the stress, which keeps sending fresh signals.

Relaxing does not work the same for everyone: in a small study of 14 tense adults, about a third felt more tense during muscle relaxation, and about half during focused meditation. Muscle relaxation caused fewer of these reactions than meditation did, which is useful to know when choosing a method.

Newer work hints at why: people prone to worry may resist the sudden drop in guard that relaxing brings. That came from a study of 96 students, so it is a clue rather than a settled answer.

The largest review found that switching off after work tracked with better mood and sleep, but not with hormone or heart measures. How closely the body follows the feeling is still an open question.