Carpal tunnel syndrome (CTS) is the most common peripheral nerve entrapment in adults. Cleveland Clinic estimates it affects roughly 3% of US adults per year, and globally prevalence estimates run as high as 5%. The distinctive feature is that 80% of patients experience symptoms at night — waking up with a hand that feels dead or with pins-and-needles severe enough to interrupt sleep. Symptoms usually improve with shaking the wrist and can disappear during the day, only to return the next night. The affected fingers are the thumb, index, middle, and half of the ring finger — the specific territory of the median nerve.

The mechanism is elegant. When your wrist is flexed or extended during sleep, pressure inside the carpal tunnel — the narrow passage under the ligament at the base of the palm — rises significantly. The median nerve, which runs through this tunnel, gets compressed. Fluid redistribution when you lie down further raises the pressure. If you have any pre-existing swelling from arthritis, pregnancy, repetitive computer use, or metabolic conditions, the tunnel is already tight and the nightly compression pushes it over the symptomatic threshold. This is why CTS is so specifically a nighttime phenomenon — the wrist flexion of sleep, the fluid shift of lying down, and the loss of dynamic movement all compound.

The fitness-culture angle is worth flagging. Weightlifters who train grip-heavy movements, cyclists who spend hours with wrists extended on the hoods, and heavy computer users all elevate their baseline CTS risk. So do keyboard-heavy jobs. Some studies report that up to 30% of frequent computer users have at least intermittent hand paresthesias, though only 3 to 5% meet full diagnostic criteria on nerve conduction studies. The takeaway is that CTS is not just a “middle-aged office worker” condition. Anyone whose hands fall asleep at night regularly and who has repetitive wrist loading in their daytime life should treat this as their most likely lane.

Cubital tunnel syndrome is the second most common peripheral nerve entrapment after CTS, and it is systematically misdiagnosed as carpal tunnel because the symptoms are similar. The distinguishing feature is finger pattern: cubital tunnel affects the ring finger and pinky, not the thumb-index-middle. If your pinky is the finger that goes numb at night, this is your lane, not CTS. The University of Utah now informally calls this condition “cell phone elbow” because prolonged elbow flexion — from holding a phone, sleeping with the arm bent, or leaning on the elbow at a desk — is the primary driver.

The ulnar nerve runs behind the medial epicondyle (the “funny bone” area) and gets stretched and compressed when the elbow is flexed beyond 90 degrees. During sleep, most people naturally curl their arms with elbows bent, tucking hands under the pillow or against the chest. Hold that position for 6 to 8 hours and the ulnar nerve loses blood flow and starts firing pain signals. The classic pattern is waking with the pinky and ring finger asleep, sometimes accompanied by an achy sensation on the inside of the elbow. Long-term untreated cases can produce visible hand weakness and difficulty with fine motor tasks.

The third cause originates upstream — at the neck. When a cervical spine nerve root gets compressed or irritated by disc bulging, arthritis, or muscular tension, the sensory signal referred pattern radiates down the arm and into specific fingers depending on which vertebral level is affected. C6 radiculopathy sends symptoms to the thumb and index finger, C7 to the middle finger, C8 to the ring and pinky. So the finger pattern here can mimic either carpal tunnel or cubital tunnel — but the distinguishing feature is neck involvement. If you also have neck stiffness, pain that radiates from the neck down into the arm, or symptoms that change based on head position, this is your lane.

The desk work era has made this dramatically more common. Chronic forward head posture — the classic “text neck” — puts sustained compression on the lower cervical discs and produces both muscular tightness and disc bulging over time. Sleep position amplifies the problem: sleeping with a pillow too high or too low bends the neck sharply, which either compresses or stretches the nerve roots for hours. People who consistently notice one-sided arm numbness that correlates with the side they slept on, especially if paired with morning neck stiffness, are usually dealing with cervical radiculopathy rather than isolated wrist compression.

The fourth cause is not a compression problem at all — it is a nerve health problem. Vitamin B12 deficiency causes peripheral neuropathy through disruption of myelin synthesis, the protective coating around nerves. Without adequate B12, myelin degrades, nerves misfire, and the classic clinical picture is tingling and numbness that starts in the fingertips and toes — a “stocking and glove” pattern that does not match any single nerve territory. Unlike compression neuropathy, this pattern does not improve with shaking or splinting. It progresses slowly, symmetric, both hands and often both feet.

Prevalence data: B12 deficiency affects roughly 1.8% of general US adults, but rises to 5.8% in adults over 50, 30 to 40% in vegetarians and vegans, and 14 to 23% in patients on long-term metformin (a common diabetes medication). Diabetic peripheral neuropathy is a parallel and even more common cause — roughly 50% of people with type 2 diabetes will develop some degree of peripheral neuropathy, and hand and foot symptoms are typically the first sign. If your finger numbness doesn’t match a clear nerve territory, doesn’t respond to shaking, involves both hands, or gets worse when you’re tired, ask a physician for a B12 level and, if appropriate, a fasting glucose or HbA1c.

One additional metabolic driver worth knowing: hypothyroidism. Underactive thyroid function can cause both direct peripheral nerve dysfunction and secondary carpal tunnel syndrome through fluid retention that narrows the carpal tunnel. Hypothyroidism affects roughly 5% of US adults and is particularly common in women over 40. If your hands fall asleep at night is one of several unexplained symptoms alongside fatigue, cold intolerance, unexplained weight gain, and dry skin, a thyroid panel (TSH, free T4) should be included in your workup. The three metabolic causes — B12, diabetes, and thyroid — overlap in their clinical picture but are all inexpensive to test for and highly treatable once identified.