Why Your Hands Go Numb While You Sleep

You wake up in the dark, and your hand feels like it belongs to someone else. It is heavy, tingling, maybe completely dead from the wrist down. You shake it, flex your fingers, and after a minute or two the pins-and-needles fade. You roll over and forget about it until it happens again next week.

This is one of the most common nighttime complaints doctors hear, and most of the time it has a simple explanation: you slept on a nerve. But occasionally, numb hands at night are an early warning of something that deserves attention. Here is how to tell the difference, and how to stop it.

Why a sleeping position can cut off a nerve

Nerves are not like wires buried deep inside a wall. In several spots around your arm and wrist, they run close to the surface, where a mattress, a pillow, or your own body weight can squeeze them for hours.

Three nerves do most of the work in your hand, and each one produces a different pattern of numbness:

• The median nerve runs through the carpal tunnel, a narrow passage in your wrist. When it is compressed, your thumb, index finger, middle finger, and half of your ring finger go numb or tingly. This is the classic carpal tunnel pattern.
• The ulnar nerve runs through a groove on the inside of your elbow, the spot you know as your "funny bone." Bend your elbow sharply all night, or rest it on a hard surface, and your pinky and the other half of your ring finger fall asleep.
• The radial nerve wraps around the upper arm. Fall asleep with your arm draped over the back of a chair or a couch arm, and you can wake up with a weak, numb wrist and hand, sometimes called "Saturday night palsy."

When a nerve is compressed, it stops sending signals properly. That is why the hand feels dead rather than painful. Brief compression, the kind that happens during a night's sleep, almost always reverses on its own within minutes of changing position.

The usual suspects: how you actually sleep

Most nighttime numbness comes down to a few habits:

Sleeping on your side with your arm under your head. This is the number one cause. Your head weighs 10 to 11 pounds, and when it rests on your arm for hours, it compresses the nerves at the elbow and wrist. Side sleepers who tuck a hand under their pillow are especially prone to it.

Sleeping with your wrists bent. If your hands curl inward or your wrists fold under your pillow, pressure builds inside the carpal tunnel. People who sleep on their stomachs with their hands tucked under them often report exactly this pattern.

A mattress or pillow that is too firm, or too soft. A pillow that is too high bends your neck and shoulders into a position that narrows the space nerves pass through. A mattress that lets your shoulder sink too far can do the same thing from the other direction.

Your partner's arm. "Honeymoon palsy," numbness from a partner sleeping on your arm, is a real and well-documented phenomenon. The weight is the same as your own head, and the effect is identical.

When it is more than a sleep position

Position-related numbness follows a clear pattern: it happens on the side you slept on, fades within minutes of waking, and leaves no daytime weakness. If your symptoms break that pattern, something else may be going on.

Carpal tunnel syndrome. About 1 in 20 American adults has carpal tunnel syndrome, and it is the most common cause of persistent nighttime hand numbness. The telltale signs: numbness that wakes you almost every night, symptoms in both hands, pain shooting up the forearm, and dropping things in the morning because your grip feels clumsy.

Diabetic peripheral neuropathy. The Centers for Disease Control and Prevention estimates that about half of people with diabetes develop some form of nerve damage. It usually starts in the feet, not the hands, and causes constant tingling or burning rather than position-dependent numbness. But if you have diabetes and your hands are going numb, mention it to your doctor.

Vitamin B12 deficiency. B12 keeps your nerves insulated, and low levels can cause tingling in the hands and feet. It is more common in adults over 50, in people who eat little or no animal products, and in people who take metformin or acid-reducing medicines long term. A simple blood test checks it.

Pregnancy. Swelling during pregnancy, especially in the third trimester, narrows the carpal tunnel and causes nighttime hand numbness in many expectant mothers. It usually resolves after delivery.

How to stop it tonight

If your numbness fits the position pattern, a few changes often fix it within a week:

• Do not sleep on your arm. Hug a body pillow instead of tucking your arm under your head or pillow. If you are a dedicated side sleeper, a pillow thick enough to keep your head level with your spine, usually 4 to 6 inches for most adults, keeps your shoulder and arm in a neutral position.
• Keep your wrists straight. A soft wrist splint worn at night holds the wrist in a neutral position and takes pressure off the median nerve. Drugstores sell them for under 20 dollars, and they are the first treatment most doctors recommend for carpal tunnel symptoms.
• Stretch before bed and shake it out. Gently extend each wrist for 15 seconds, then flex it the other way, five times per hand. When you wake up numb, shake the hand vigorously and flex your fingers to restore feeling faster.

When to see a doctor

Make an appointment if any of these apply:

• Numbness happens most nights for more than two weeks despite changing your sleep position.
• Both hands are affected, or the numbness does not fully go away during the day.
• You have weakness, such as dropping cups, trouble buttoning a shirt, or difficulty opening jars.
• Numbness comes with pain in the neck, shoulder, or arm, or with swelling, color changes, or sores on the hands.
• You have diabetes, or you notice tingling in your feet as well as your hands.

A doctor can usually diagnose the cause with a physical exam and, if needed, a nerve conduction study, a painless test that measures how well signals travel through the nerve. Carpal tunnel syndrome caught early often responds to a night splint and activity changes; advanced cases may need a minor outpatient procedure.

The bottom line

Waking up with a dead hand is startling, but in most cases it is your body telling you that you slept in a bad position, not that something is seriously wrong. The pattern is your best clue: numbness that matches the side you slept on and fades within minutes is almost always positional. Numbness that shows up every night, affects both hands, or lingers into the day deserves a doctor's look.

Try the simple fixes first: a body pillow, a neutral wrist position, and a night splint if the thumb-side fingers are the ones going numb.