Waking up with numb arms, especially after sleeping with them elevated, is a common experience. This temporary sensation, often described as tingling “pins and needles,” usually resolves quickly when you change position. Understanding the physiological reasons behind it can help explain why it happens.
Understanding the Numbness
The sensation of numbness, tingling, or “pins and needles” is medically known as paresthesia. This phenomenon arises from the temporary compression of nerves or blood vessels. When a nerve is compressed, it disrupts signal transmission, leading to altered sensations like tingling or numbness.
Blood vessel compression also contributes by reducing blood flow, a condition called ischemia. When blood flow is restricted, tissues, including nerves, are deprived of oxygen and nutrients. This temporary deprivation causes nerves to malfunction, resulting in numbness and tingling until circulation is restored. The body often prompts a change in position to alleviate this pressure.
Specific nerves are more susceptible to compression depending on the location. The median nerve, for instance, controls sensation in the thumb, index, middle, and part of the ring finger, and its compression can lead to numbness in these areas. The ulnar nerve, which runs along the inside of the elbow, affects the ring and little fingers, and prolonged bending of the elbow can compress it. The radial nerve, controlling the back of the hand and thumb, can experience compression when the arm is outstretched or under the head.
Sleeping Positions and Nerve Compression
Sleeping with arms above the head increases the likelihood of nerve and blood vessel compression. This elevated position can stretch nerves or compress them in confined spaces like the thoracic outlet. The thoracic outlet is a narrow area between the collarbone and first rib, through which nerves and blood vessels pass to the arm. Compression here, known as thoracic outlet syndrome, can be exacerbated by certain sleeping postures.
The weight of the head or torso, when placed on an arm, applies pressure to nerves and arteries. For example, resting the head on an outstretched arm can compress the radial nerve, causing numbness along the back of the arm, forearm, and hand. Sleeping on the stomach with hands above the head or wrists flexed can also cause nerve compression. Prolonged wrist flexion, common in these positions, can increase pressure on the median nerve within the carpal tunnel.
Maintaining a static position for extended periods during sleep can lead to sustained pressure on nerves, impairing blood flow and altering nerve conduction. This continued stress can result in tingling and numbness upon waking. When the elbow is bent for long periods, such as with hands by the face, it can irritate the ulnar nerve.
Strategies to Prevent Numbness
Adopting different sleeping habits can prevent arm numbness. Changing sleeping positions is an effective approach to reduce nerve pressure and improve circulation. Sleeping on your back with arms at your sides is a beneficial position, as it minimizes compression. If on your back, placing a pillow under each elbow can help keep shoulders relaxed and arms neutral, discouraging elevation.
For side sleepers, placing a pillow between the knees can help maintain spinal alignment. Hugging a pillow can support the upper arm, preventing it from tucking under the body and compressing nerves in the shoulder, elbow, or wrist. Avoid sleeping directly on an arm or with hands tucked under the pillow.
Ensuring proper spinal alignment with supportive pillows and a comfortable mattress can also prevent numbness. A pillow that cradles the neck without positioning the head too high or low can protect nerves traveling from the spine into the arms. Keeping wrists neutral and unflexed while sleeping, possibly with a wrist brace for conditions like carpal tunnel syndrome, can also alleviate nerve pressure.
When to Seek Medical Advice
While temporary arm numbness during sleep is often harmless and resolves on its own, certain indicators suggest seeking medical advice. Consult a healthcare professional if the numbness is frequent, persistent, or occurs regardless of sleeping position. This is especially true if accompanied by symptoms like pain, weakness, or muscle loss in the arm or hand.
Other concerning signs include numbness that interferes with daily activities or sleep, or difficulty moving the arm or hand. If numbness begins suddenly, is severe, or is associated with confusion, trouble talking, dizziness, or a sudden, severe headache, seek immediate medical attention. These symptoms could indicate more serious underlying conditions, such as cervical radiculopathy (a pinched nerve in the neck), carpal tunnel syndrome, or circulatory issues or neurological conditions.