Shoulder pain that intensifies or only appears when lying down is a common and disruptive problem. This nocturnal discomfort occurs because the horizontal position alters mechanical forces and concentrates inflammatory responses. When lying down, the shoulder structures shift, and body weight against the mattress compresses internal tissues. Understanding the causes of this symptom is the first step toward finding relief and restoring restful sleep.
Underlying Structural Injuries
Structural damage to the shoulder joint frequently causes pain that worsens at night due to direct pressure. The rotator cuff, which is a group of four tendons and muscles stabilizing the shoulder, is particularly susceptible to this mechanical aggravation. Rotator cuff tendinopathy or tears cause pain at rest, and lying on the affected side compresses the damaged tendon tissue against the bone. The slowing of circulation and muscle relaxation during sleep can also make underlying inflammation and injury more apparent.
Shoulder impingement syndrome is another common mechanical issue where tendons become compressed within the subacromial space. This narrow area sits beneath the acromion, the bony tip of the shoulder blade. When a person lies on their side, the pressure pushes the upper arm bone (humerus) closer to the acromion, narrowing this space further and pinching the irritated rotator cuff tendons or bursa. This direct mechanical compression explains why the pain is often immediately triggered upon shifting onto the painful side.
The pain is often described as a dull, persistent ache that makes it difficult to fall asleep or causes frequent awakenings. Damage to the fibrocartilage ring around the shoulder socket, known as a labral tear, can also be aggravated by positional pressure. While labral tears are typically associated with clicking or catching, lying on the shoulder places extra stress on the torn tissue.
Positional Compression and Inflammation
Beyond structural tears, nighttime pain is often caused by inflammation sensitive to pressure and external mechanical forces. Bursitis, the inflammation of the fluid-filled sacs (bursae) that cushion the joint, is a prime example of a condition worsened by pressure. The subacromial bursa, located above the rotator cuff tendons, becomes highly sensitive when inflamed. Lying on the side applies the full weight of the torso directly onto the inflamed sac, intensifying the pain and resulting in sharp discomfort.
Sleeping posture plays a significant role in causing or aggravating shoulder pain. Side sleeping is the most common culprit, forcing the shoulder to bear the weight of the upper body and leading to joint compression. Awkward positions, such as sleeping with the arm held overhead, create unnatural stress points that irritate nerves and soft tissues. Additionally, a mattress that is too firm or too soft can cause poor spinal and shoulder alignment, contributing to increased tension overnight.
Another source of nocturnal shoulder pain is referred pain, which originates outside the joint. Issues in the cervical spine, such as a pinched nerve or degeneration in the neck vertebrae, can radiate pain into the shoulder. If the sleeping position causes the neck to be hyperextended or twisted, it can compress a nerve root. This compression leads to a burning or sharp pain that travels down into the shoulder and arm.
When to See a Doctor
While minor shoulder aches often resolve with rest and positional adjustments, certain signs indicate the need for a professional medical evaluation. Consult a doctor if the pain persists for more than a few weeks despite at-home care, or if the pain progressively worsens. Immediate medical attention is necessary if the pain follows an acute traumatic event, such as a fall or sudden injury. Signs of a more severe problem include sudden, significant weakness or the inability to lift the arm. Systemic symptoms accompanying the pain are considered red flags, including fever, chills, rapid swelling, or extensive redness, which could indicate a serious infection.