Headaches, nausea, and fatigue are unpleasant symptoms on their own, and sometimes they occur together.

People can usually manage these symptoms at home with conservative treatments, but, occasionally, they can signal an underlying health condition.

In this article, learn about the causes of a headache, nausea, and fatigue, as well as about the possible treatments.

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Mild dehydration is a possible cause of a headache, nausea, and fatigue.

Headaches, nausea, and fatigue can be triggered separately by common factors, such as:

  • mild dehydration
  • disturbed sleep
  • stress

Often, once a person deals with the underlying cause by drinking enough water or getting a good night's rest, the headache, nausea, and fatigue will disappear.

However, there are several conditions that can cause headaches, nausea, and fatigue that may require medical attention. Some are more common than others.

Influenza

Influenza, or the flu, is a very common viral illness. Symptoms of the flu include:

  • fever
  • cough
  • sore throat
  • headaches
  • fatigue
  • achy muscles
  • runny or stuffed up nose
  • nausea, vomiting, and diarrhea (more common in children)

Most people who contract the flu recover within 2 weeks. However, some people are at risk of developing complications, such as sinus infections and pneumonia. These groups of people include:

  • people over 65 years of age
  • people with pre-existing health conditions, such as asthma or heart disease
  • pregnant women
  • children under 5 years of age

Migraine

According to the American Migraine Foundation, migraine affects 37 million people in the United States.

There are several stages of a migraine episode:

  • Prodrome, or "pre-headache," which can last a few hours to several days.
  • Aura, which can include blurry vision or blind spots, lasting up to 1 hour.
  • Headache on one or both sides of the head, lasting up to 3 days.
  • Postdrome, or "migraine hangover," lasting up to 2 days.

Throughout these stages, a person can experience several symptoms, along with headaches, nausea, and fatigue. Some of these include:

  • sensitivity to light and sound
  • trouble sleeping
  • irritability
  • vomiting
  • inability to concentrate

There are medications available for migraines, split into two categories. These categories are for acute or preventative treatment.

A person takes acute medication at the first sign of a migraine attack, whereas they take preventative medication regularly to try to reduce the number and severity of migraines.

Chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a complex condition that may stop people from taking part in their usual activities.

It affects an estimated 836,000 – 2.5 million people in the U.S. alone. Doctors do not currently know what causes the condition.

As well as fatigue, headaches, and nausea, signs of CFS can include:

  • flu-like symptoms
  • achy muscles
  • difficulty getting to sleep or waking up
  • sensitivity to light and sound
  • loss of appetite

There is currently no cure for CFS. However, doctors will work with people to address their main symptoms.

The Centers for Disease Control and Prevention (CDC) also recommend professional counseling and other complementary therapies, as well as following a healthful, balanced diet.

Less common causes

Other, less common causes of headache, nausea, and fatigue include:

  • yellow fever, which is more common in tropical and subtropical regions
  • postural tachycardia syndrome, which occurs when rising from a seated or reclining position
  • heatstroke, which happens due to exposure to heat
  • Addison's disease, a hormonal condition
  • pregnancy, which may cause these symptoms due to hormone changes

Headaches, nausea, and fatigue are very common symptoms of other health conditions. As such, it is difficult to determine whether these symptoms can directly affect each other.

A 2014 study on nausea in people with migraine suggests that these symptoms may come from different parts of the brain.

The researchers found that the areas of the brain relating to nausea showed an increase in activity before headaches occurred.

Also, nausea became worse when headaches appeared, possibly due to connections between the two areas responsible for these symptoms activating.

The authors concluded that although headaches can make nausea worse, neither of these symptoms directly causes the other.

There are many reasons why a person may experience fatigue.

A 2017 study suggested that migraines and fatigue, as a symptom of depression, may be linked by a dysfunction of the hypothalamus. However, it is not clear whether headaches cause fatigue or vice versa.

Research has found a similar link between conditions that cause fatigue, such as fibromyalgia and migraines.

One study found that more than half of 1,730 people with fibromyalgia also experienced migraine episodes, suggesting a link between fatigue and headaches.

A 2019 study found that more than a third of people who have CFS also experience migraines headaches. As CFS affects the nervous system, it may have a knock-on effect on blood vessels, leading to migraine headaches.

However, this study only surveyed 150 people, so the sample may not be reflective of a larger population.

A 2018 study has suggested that hypotension may be the common link between fatigue and nausea in people with CFS.

Hypotension, or low blood pressure, may trigger an autoimmune response. This response may, in turn, trigger symptoms such as nausea and fatigue in those who have CFS.

Headaches, nausea, and fatigue have many links, but it is difficult to prove that one causes the other.

Headaches can have many causes, such as stress or dehydration. Similarly, any number of everyday triggers can cause nausea and fatigue.

However, it is important to see a doctor if these three symptoms are severe, long lasting, or affect daily activities.

When headaches, nausea, and fatigue appear together, they may be symptoms underlying another health condition.

Headaches, nausea, and fatigue have many causes. When they appear together, they can be symptoms of conditions such as the flu, migraines, or CFS.

While occasionally experiencing these symptoms is usually nothing to be concerned about, people should see a doctor if they are affecting daily activities.

Studies have shown links between the three symptoms, but, as these symptoms often present together in multiple health conditions, it can be difficult to determine whether they can cause each other.