Why Does My Shoulder Hurt When I Sleep On My Side? | Causes, Injuries, and Prevention Tips

Written by on November 11, 2021 — Medically reviewed by John Doe

Why Does My Shoulder Hurt When I Sleep On My Side

If you’ve ever asked yourself, “why does my shoulder hurt when I sleep on my side?” you’re not alone. The CDC says that about 35% of people in the US report sleep deprivation. (1) And pain, as you might very well know, is one of the prime reasons.

 There are several reasons for this, too. This includes prolonged compression and shoulder injuries.

We’ll talk about them in deeper detail further down. I’ll give you some tips on how to prevent them as well. Let’s get to it!

3 reasons why sleeping on your side leads to shoulder pain

1. Inflammation

Inflammation is a sign of damage and overexertion. For example, when you do a new workout regiment or if you’re still using your already sore shoulders more than you should.

Since we’re in a fixed position when we sleep, inflammation runs up and around our shoulders and other parts of the body.

Also, shoulder pain from sleeping on your side increases subacromial pressures.

This, in turn, can further damage your already inflamed tendons. (2) And, again, contribute to why you experience shoulder pain at night.

2. Poor alignment

Let’s do a little math: According to the CDC, the average adult sleeps for around 7 hours per day. (3)

Half of the time we sleep, we lay on our sides.  So for about 3 and a half hours, we rely on our head pillow and shoulder joint to keep us stable and comfortable. (4)

With poor alignment to your head and neck, the muscles in your upper body need to compensate. This contributes to why you experience neck stiffness, upper back spasms, and shoulder pain in the middle of the night.  

3. Compression

When you sleep on your side, you’re also pressing down on your shoulder joint for an extended period. This can decrease blood flow to your shoulder blade, rotator cuff, and down to your arm.

For some, it leads to that familiar pins and needles sensation that can easily go away with changing positions. But for others, it can also aggravate existing rotator cuff injuries that can bring about positional shoulder pain.

Speaking of injuries, you might be asking, “what conditions make my shoulder joint feel worse when on a side-sleeping position?”

3 shoulder injuries with side-lying shoulder pain

1. Frozen Shoulder

Constant inflammation within your joint capsule can lead to a frozen shoulder (adhesive capsulitis). This leads to progressive shoulder pain and stiffness. If it gets worse, it can even cause nighttime shoulder pain.

But, why is that?

Our upper arm bone is enclosed by our joint capsule, making arm movements smooth and stable. With a frozen shoulder, the size of our capsule decreases, making a vice-like grip on our affected arm.

When you sleep on your affected shoulder, you are compressing the head of your upper arm bone to your already inflamed capsule.

This can trigger a strong pain reaction and an unpleasant stinging sensation from your shoulders down to your arms. 

Further reading: Here’s our complete guide to frozen shoulders.

2. Shoulder impingement syndrome

Your rotator cuff holds your arm in place. But, poor biomechanics can make your rotator cuff tendons hit and/or rub against your shoulder blades. It can lead to a vicious cycle of shoulder pain whenever you lift your arms.

Since subacromial pressure is much higher for side-sleepers, it decreases blood flow to your tendons. By not giving your tendons a good environment to heal, inflammation and pain may continue to get worse.

3. Rotator cuff tear

Some signs and symptoms indicate there’s a rotator cuff tear present. Like a recent trauma on your shoulder or previous episodes of rotator cuff tendonitis.

This rotator cuff injury causes debilitating pain that may need surgery.  So why does sleeping on your side cause so much pain? There’re two things to consider:

  • First, you have a torn tendon. That itself is painful. Compressing it against your body for a long period is even worse.
  • Second, your other shoulder muscles are working even harder to compensate and stabilize your arm. Side-lying with poor alignment can increase tension and lead to muscle spasms and pain.

Try this: Tips for sleeping with a rotator cuff tear

5 Tips on how to avoid shoulder pain from side-sleeping at night

1. Change your sleeping position

Fun fact: Most people frequently sleep on the side of their injury. (5)

So, to avoid shoulder pain, simply sleep on the side opposite your injury. You can also sleep on your back.

I admit that it may take some time to get used to. But changing your sleeping position will bring much-needed pressure relief and alleviate pain in your shoulder.

Related: The healthiest sleeping positions for shoulder pain.

2. Use more pillows

Aside from comfort, using more pillows can help align and stabilize your upper body. (6)

That is, of course, if you use them to promote better alignment.

For side-sleepers, adding a pillow between your knees and under your head helps keep your spine and pelvis in a more neutral position. This, in turn, helps reduce night-time shoulder pain.

3. Try a different type of pillow

Have you ever heard of a pillow made out of rubber?

This was from a study comparing different types of pillows. Among others, a rubber pillow is found to be the most comfortable and helps improve sleep quality. Also, it reduces the incidence of shoulder pain from sleeping. (7)

4. Pain medication

There are different anti-inflammatory medications that you can take a few hours before you sleep. It will provide pain relief so that you can still sleep on your side undisturbed.

5. Physical Therapy

If you want long-lasting relief, then book an appointment at your local PT clinic. They’ll help figure out what’s wrong with your shoulder and guide you on how to prevent shoulder pain from sleeping.


Will the type of foam in my mattress affect my shoulder pain?

Yes, your mattress affects your shoulder pain.

The softer the foam, the easier it will be for your spine and upper body to sag down. (8)

This malalignment can lead to muscle spasms and pain.

But, a hard mattress will also put more pressure on your joints, causing shoulder pain.

So, if you prefer sleeping on your side, try out different mattresses that feel firm enough to support your weight in that position.

Does sleeping on your side affect digestion?

Certain sleeping positions are more beneficial than others. Sleeping on your left side can affect your gut health. To be more specific, it helps reduce the incidence of heartburn. (9)

Our stomach is asymmetric. It has a much larger space on the left side compared to the right. So, when you turn your body to the left, the gastric acid in your stomach will have a much harder time going over your stomach valve.

This prevents gastric acid from back flowing down to your esophagus.


Happiness and self-love start with a good night of sleep. With just a few minor adjustments, you’re on your way to a better and productive day!

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  1. “Sleep and Sleep Disorders”. Centers for Disease Control and Prevention. Accessed 03 Nov 2021. https://www.cdc.gov/sleep/data_statistics.html
  2. Longo, Umile Giuseppe et al. “Sleep Disturbance and Rotator Cuff Tears: A Systematic Review.” Medicina (Kaunas, Lithuania) vol. 55,8 453. 8 Aug. 2019, doi: 10.3390/medicina55080453
  3. “How Much Sleep Do I Need?”. Centers for Disease Control and Prevention. Accessed 03 Nov 2021. https://www.cdc.gov/sleep/about_sleep/how_much_sleep.html
  4. De Koninck, J et al. “Sleep positions and position shifts in five age groups: an ontogenetic picture.” Sleep vol. 15,2 (1992): 143-9. DOI: 10.1093/sleep/15.2.143
  5. Zenian, John. “Sleep position and shoulder pain.” Medical hypotheses vol. 74,4 (2010): 639-43. DOI: 10.1016/j.mehy.2009.11.013
  6. Liu, Shuo-Fang et al. “Shape design of an optimal comfortable pillow based on the analytic hierarchy process method.” Journal of chiropractic medicine vol. 10,4 (2011): 229-39. doi: 10.1016/j.jcm.2011.04.002
  7. Gordon, Susan J et al. “Pillow use: the behavior of cervical pain, sleep quality and pillow comfort in side sleepers.” Manual therapy vol. 14,6 (2009): 671-8. DOI: 10.1016/j.math.2009.02.006
  8. Wong, Duo Wai-Chi et al. “Sleeping mattress determinants and evaluation: a biomechanical review and critique.” PeerJ vol. 7 e6364. 25 Jan. 2019, doi: 10.7717/peerj.6364
  9. Person, Erik et al. “A Novel Sleep Positioning Device Reduces Gastroesophageal Reflux: A Randomized Controlled Trial.” Journal of clinical gastroenterology vol. 49,8 (2015): 655-9. DOI: 10.1097/MCG.0000000000000359