Many things can cause sudden onset joint pain and fatigue, including flu and some types of arthritis. In some cases, aching bones and tiredness are symptom of a chronic condition.

“Sudden onset” means the symptoms begin without warning. Sudden onset does not always mean something is seriously wrong, though.

This article will discuss seven causes of joint pain and fatigue that can come on quickly. It will explain what they are, their symptoms, and their treatments.

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Influenza, or flu, is a viral infection. It affects the nose, throat, and, in some cases, the lungs. It is contagious and transmits through coughs and sneezes.

The symptoms of flu often come on suddenly and include fatigue, joint pain, and body aches. Other symptoms include:

People with mild to moderate symptoms usually recover without treatment within 2 weeks. In these cases, over-the-counter (OTC) cold and flu medications can help ease symptoms.

In more severe cases, or in people who are vulnerable to flu complications, doctors may recommend antiviral drugs to shorten the illness. A person needs to start antivirals within 1–2 days of the symptoms starting for this to work. The best way to prevent the flu is with annual vaccination.

COVID-19 can also cause joint pain and fatigue. If there is a chance a person may have COVID-19, they need to stay at home and follow local authority guidelines for getting tested.

Learn more about COVID-19 and joint swelling.

Aching and tiredness are common side effects of some vaccines, such as the COVID-19 vaccine. The symptoms can come on suddenly in the period shortly after getting the vaccine.

Other potential side effects include:

  • mild fever
  • pain at the injection site
  • chills
  • headache

These side effects tend to be mild and will usually go away on their own.

Rheumatoid arthritis (RA) is an autoimmune condition that develops when the immune system attacks its own joint tissue. It can develop in any joint in the body, but often affects several joints at once.

The symptoms of RA, which include joint pain and fatigue, can come and go. They may come on suddenly during a flare-up. Other symptoms include:

  • swelling or stiffness in more than one joint
  • symmetrical symptoms that affect both sides of the body
  • fever
  • weakness
  • unexplained weight loss

Treatment for RA involves medications that slow the disease and prevent damage to the joints. People can also benefit from lifestyle strategies that reduce pain and improve quality of life.

Reactive arthritis is the result of an infection. For example, if someone has a sexually transmitted infection or food poisoning, the bacteria that are causing it can get into the bloodstream. This can lead to inflammation in different parts of the body, including the joints.

Reactive arthritis can also affect the eyes and urinary tract. Some people may experience redness, pain, or irritation in the eyes. Sometimes, it can cause pain when urinating.

Symptoms will usually develop between 1–6 weeks after contracting an infection. The symptoms may come and go for several weeks to several months.

The bacteria most associated with reactive arthritis are:

Doctors usually recommend antibiotics to clear the infection. They may also suggest nonsteroidal anti-inflammatory drugs (NSAIDs) to help with the pain, such as:

Sometimes, joint pain and fatigue are among the first symptoms of lupus. Lupus is an autoimmune condition that affects different parts of the body, including the:

  • skin
  • joints
  • internal organs

Symptoms include:

  • swelling in the hands or feet
  • swelling around the eyes
  • headache
  • mild fever
  • sensitivity to light
  • pain in the chest during deep breaths

People may also notice a rash shaped like a butterfly on the cheeks and nose, hair loss, or mouth or nose sores. The symptoms usually come and go over time.

There is no cure for lupus, but doctors can help people manage their symptoms. They may recommend NSAIDs or corticosteroids to ease the inflammation. People sometimes use antimalarial drugs to help with joint pain and fatigue.

Septic arthritis occurs when bacteria from an infection elsewhere in the body get into joints. This can also happen after an injury or surgery. It is a potentially serious condition that can be life threatening without treatment.

The symptoms include:

  • severe joint pain that starts suddenly, usually in just one joint
  • joint swelling
  • skin color changes around the joint
  • fever or chills
  • feeling generally unwell

People with these symptoms should seek medical treatment as soon as possible.

Symptoms of septic arthritis often develop quickly over a few days. Doctors treat it with intravenous antibiotics, which involves staying in a hospital. A doctor may also drain the fluid from around the joint, or give oral antibiotics for a person to take at home.

Brucellosis is an infectious disease that occurs from bacteria. People may develop the condition after being in contact with infected animals or animal products. The most commonly affected animals include:

  • sheep
  • cattle
  • goats
  • pigs
  • dogs

Possible symptoms include joint pain and fatigue as well as:

  • fever
  • headache
  • not wanting to eat
  • muscle pain
  • back pain

Doctors usually recommend antibiotics to treat the infection.

Other potential causes of aching bones and tiredness include:

This is not an exhaustive list.

Some causes of aching joints and fatigue, such as mild flu or mild vaccine side effects, get better on their own. Others, such as reactive arthritis, RA, or lupus, will need treatment.

The Arthritis Foundation recommends people talk with a doctor if they experience joint problems that last for 3 days or more, or several episodes of joint symptoms within a month.

Seek immediate help for severe or worrying symptoms, such as:

  • difficulty breathing
  • chest pain or pressure
  • blue, gray, or white lips and nails
  • new confusion
  • difficulty staying awake
  • severe muscle pain
  • severe weakness or loss of balance
  • lack of urination
  • seizures
  • flu-like symptoms that get better but then come back

Additional signs a child may need emergency medical care include:

  • a fever of over 104°F (40°C), or any fever in children younger than 12 weeks
  • ribs pulling with each breath
  • lack of alertness or interaction when awake
  • refusing to walk
  • dry mouth
  • no urine for 8 hours, or no tears when crying

Lots of things can cause sudden joint pain and fatigue. They include flu and vaccine side effects. Sometimes, long-term conditions, such as RA or lupus, can cause aching bones and tiredness.

The best treatment will depend on the cause. Mild flu and vaccine side effects will usually go away on their own. Long-term health conditions require more specialized care.

A person can contact a doctor about any unexplained joint pain and fatigue, particularly if it is severe, does not go away, or gets better and then comes back.