Whole-body shaking is your nervous system responding to a trigger, whether that’s a surge of stress hormones, a drop in blood sugar, a fever, or something else entirely. It’s one of the most common physical symptoms people experience, and in most cases it’s temporary and not dangerous. But because so many different things can cause it, understanding the pattern of your shaking helps narrow down what’s going on.
Adrenaline and the Stress Response
The most common reason for sudden, full-body shaking is an adrenaline surge. When your brain perceives a threat (real or imagined), it floods your bloodstream with epinephrine. This hormone redirects blood flow to your muscles, giving them more oxygen and fuel so they can react with greater strength and speed. The problem is that all that extra energy has nowhere to go if you’re not actually running or fighting. Your muscles contract rapidly without a clear purpose, and you shake.
This can happen during a panic attack, after a near-miss car accident, before a big presentation, or even while lying in bed replaying a stressful conversation. The shaking often comes with a racing heart, sweaty palms, and a jittery, wired feeling. It typically passes within 20 to 30 minutes as your body clears the adrenaline. Deep, slow breathing and gentle movement like walking can help speed the process along.
Low Blood Sugar
Shakiness is one of the earliest warning signs that your blood glucose has dropped too low. Symptoms generally kick in when levels fall below 70 mg/dL. Your body releases adrenaline in response to the low sugar, which is why the shaking from hypoglycemia feels so similar to anxiety: trembling hands, a pounding heart, sweating, and irritability.
You don’t need to have diabetes for this to happen. Skipping meals, exercising hard without eating, or drinking alcohol on an empty stomach can all push your blood sugar low enough to trigger shaking. Eating something with both fast-acting sugar and protein (like peanut butter on crackers or a banana with nuts) usually resolves the symptoms within 15 minutes. If you notice this pattern repeatedly, it’s worth having your fasting glucose checked.
Fever and Rigors
When your body is fighting an infection, your brain’s thermostat (located in the hypothalamus) resets to a higher temperature. To reach that new set point, your brain sends signals through the central nervous system that trigger rapid, involuntary contractions in your skeletal muscles. This is shivering, and during a fever it can be intense enough to feel like your entire body is convulsing. The medical term for this dramatic, teeth-chattering shaking is “rigors.”
Rigors are driven by the same neural circuits that make you shiver in cold weather. Your brain essentially tricks your body into thinking it’s freezing, even though your actual temperature may already be elevated. The shaking generates heat, pushing your internal temperature up toward the new set point. Once the fever peaks, the shaking usually stops. You might then start sweating heavily as your thermostat resets back down. If you have rigors with a fever above 103°F, or the fever doesn’t respond to over-the-counter fever reducers, that warrants prompt medical attention.
Medications and Substances
A surprisingly long list of medications can cause tremors or full-body shaking as a side effect. Some of the most common culprits include:
- Antidepressants (SSRIs and tricyclics)
- Mood stabilizers like lithium
- Asthma inhalers containing albuterol
- Stimulants including caffeine, amphetamines, and ADHD medications
- Steroids
- Seizure medications
- Too much thyroid medication
Caffeine is probably the single most overlooked cause. Two or three cups of coffee can be enough to produce noticeable shaking in sensitive individuals, and the threshold drops if you’re also sleep-deprived or anxious. Alcohol withdrawal is another significant trigger. If you drink regularly and suddenly stop, shaking can begin within hours and may be severe.
If you recently started a new medication or changed your dose and noticed shaking afterward, that timing is a strong clue. Don’t stop a prescribed medication on your own, but do bring it up with your prescriber.
Thyroid Problems
An overactive thyroid gland produces excess hormones that essentially speed up your metabolism. One of the hallmark signs is a fine, high-frequency tremor, most noticeable when you hold your hands out in front of you with fingers spread. But the revved-up metabolic state can make your whole body feel jittery and shaky, along with a fast heartbeat, weight loss, heat intolerance, and difficulty sleeping.
Hyperthyroidism is diagnosed with a simple blood test. If your thyroid-stimulating hormone (TSH) level is abnormally low and your free thyroid hormone levels are high, that confirms the diagnosis. It’s a treatable condition, and the shaking resolves once thyroid levels are brought back to normal.
Other Medical Causes
Several other conditions can produce generalized shaking. Your doctor may check for these depending on your symptoms and medical history:
- Low calcium, magnesium, or sodium levels can all cause muscle tremors and are detectable through basic blood work.
- Vitamin B12 deficiency affects nerve function and can produce shaking along with numbness and balance problems.
- Essential tremor, the most common movement disorder, typically starts in the hands but can spread to involve the head, voice, and trunk over time. It tends to run in families and worsens with age.
- Neurological conditions like Parkinson’s disease or multiple sclerosis can include tremor as an early symptom, though these usually come with other distinctive signs like stiffness, slowed movement, or vision changes.
When Shaking Is an Emergency
Most episodes of whole-body shaking are uncomfortable but not dangerous. However, certain features suggest something more serious is happening. Shaking that lasts longer than one minute with loss of consciousness could be a seizure rather than simple tremor. Other red flags that point toward seizure activity include loss of bladder or bowel control, tongue biting, and rhythmic convulsions that you can’t stop voluntarily.
Shaking combined with chest pain, difficulty breathing, high fever that won’t break, confusion, or slurred speech also calls for immediate evaluation. If someone near you is shaking uncontrollably and can’t respond to you, call emergency services.
What Doctors Look For
If your shaking is recurrent or doesn’t have an obvious explanation, a doctor will typically start with a detailed history: when the shaking happens, what makes it better or worse, whether it’s worse at rest or during movement, and what medications or substances you use. That history alone often points to the cause.
Initial blood work usually covers thyroid function, blood sugar, calcium, magnesium, sodium, liver function, and B12 levels. These tests rule out the most common metabolic causes. If the results are normal and the shaking persists, brain imaging with CT or MRI can help identify structural causes like a stroke or multiple sclerosis. In younger patients with unexplained tremor, doctors may also test for Wilson disease, a rare but treatable condition involving copper buildup in the body.
The type of tremor matters diagnostically. Shaking that happens at rest (when your hands are in your lap) suggests a different set of causes than shaking that only occurs when you reach for something or hold a position. Paying attention to these details before your appointment gives your doctor useful information to work with.