7 Reasons You Are Tired After Surgery

Medically Reviewed on 7/21/2022

Postsurgical fatigue introduction

When you are tired after surgery, your body is telling you to rest.
When you are tired after surgery, your body is telling you to rest.

Patients often question why they are so tired after surgery. Many patients think that because they have been "put to sleep with anesthesia" they should be refreshed and have more energy as they recover from their surgery. However, the tired feeling (fatigue) after surgery is the usual situation for most patients and there are some reasons for this outcome.

Sleep deficit

Some reasons begin even before surgery. For example, many patients have anxiety about undergoing any type of surgery and find it difficult to sleep, especially right before the date of surgery. Consequently, many patients have a sleep deficit even before they undergo surgery. This sleep deficit must be made up so the body triggers "sleepiness or fatigue" as a way to pay off this deficit.

  • Anesthetics do not make up for this sleep deficit, so the body still has it after surgery.

Anemia and blood loss

If patients have a history of anemia before surgery, they are already primed to feel tired and sleepy after surgery.

One of the consequences of low red blood count (anemia) is that the person can have fatigue. If patients have a history of anemia before surgery, they are already primed to feel tired and sleepy after surgery. Even patients who are not anemic before surgery may become anemic during or after surgery because of blood loss during and after the procedure.

In addition to feeling fatigued and/or sleepy, patients who have lost blood may have a tendency to feel weak and/or dizzy when they try to sit up or stand up. Also, they may feel fatigued because they work harder to breathe since the anemia has decreased oxygen-carrying capacity due to fewer red blood cells available to carry oxygen to the body's tissues.


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During or after surgery, several medications may be administered that are used to alter blood pressure during the procedure. Frequently used drugs are


Depression, both before and after surgery, can produce fatigue.

Depression, both before and after surgery, can produce fatigue. Some patients have fatigue caused by anxiety about pain control, surgical outcomes, concerns about new medications, the need for rehabilitation, cost of care, family situations, and many other problems. Discovering and addressing depression and anxiety before and after surgery may help reduce mental fatigue seen in some surgical patients.

Nevertheless, it is possible to reduce some of the fatigue many patients feel after surgical procedures. Keeping blood loss (anemia) to a minimum; replacing the fluid, electrolytes, and minerals quickly; avoiding potentially fatigue-inducing medications; and reducing stress (both mental and physical) before and after surgery will likely reduce fatigue. Finally, it's likely that after any surgery a person will feel some fatigue. For goodness sake, don't keep a postsurgical patient awake right after surgery with an excessive number of visitors who want to talk! Let the surgical patient rest to reduce fatigue and speed recovery.

Fasting and loss of electrolytes and minerals

Before surgery, patients are often advised to fast to avoid problems (for example, vomiting, airway compromise, aspiration of gastrointestinal contents) during anesthesia and surgery.

Fasting is often extended into the short postoperative period. This can result in a reduction or loss of electrolytes and minerals that are usually found in foods. Although fluids may be given during the surgery, they mainly supply fluid volume and do not contain all of the minerals and electrolytes that may be lost. For example, loss of sodium can cause drowsiness and muscle weakness. Loss of potassium (hypokalemia) can cause irregular heartbeats that can cause fatigue and weakness.

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Aging and overall health

With normal aging or from an overall decline in health due to progressive medical problems, there is less ability for the body to rapidly heal and cope with moderately strenuous exercises and/or activities. The result is that individuals become fatigued quicker, and the fatigue usually lasts somewhat longer.

  • Exposure to the stress of surgery (potentially new drug and/or medications, blood loss and/or anemia, electrolyte and mineral imbalances plus the new demands for the body to heal the surgical trauma) then adds to the fatigue after surgery.

Exercise and physical stress

Exercise and other activities such as strenuous work normally cause fatigue because such activity stresses the body. In order to recover, the body triggers a fatigue response so that the person will be encouraged to rest.

This is a normal stress-recovery cycle. Undergoing surgery where the body is given medications and traumatized by procedures can cause fatigue as the body enters into the repairing and healing mode.

Medically Reviewed on 7/21/2022
Lederer, E. "Hypokalemia." Medscape. Dec. 6, 2018. <https://emedicine.medscape.com/article/242008-overview>.