If you’re suffering from fatigue and constant headaches, it may be time to see a doctor.

Headache could be a sign of a migraine disorder, sleep disorder, dehydration, or several other chronic illnesses. Fatigue is a common symptom of many conditions including depression, sleep disorders, and fibromyalgia. Fatigue and lack of energy is also a frequent complaint of people who suffer from migraine headaches.

It’s possible that headaches and fatigue could be interconnected. Let’s take a closer look at the relationship between these two symptoms.

Fatigue and headache are shared symptoms of many conditions. Not all of these conditions are considered serious. However, some may require lifestyle changes or ongoing treatment.

As you consider the reasons why you may be experiencing headache and fatigue, make sure to think about your lifestyle, including your sleeping patterns, diet, and any medications you’re currently taking.

Here are 16 conditions and other factors that could cause both headache and fatigue:

Migraine is a neurological condition that causes frequent intense headaches. Migraine symptoms may start one to two days before the headache itself. This is referred to as the “prodrome” stage. During this stage, many people also experience fatigue, depression, and low energy.

When the headache hits, it’s referred to as the “attack” phase. Other symptoms include:

  • nausea
  • vomiting
  • dizziness
  • head pain
  • sensitivity to light and sound

Once the headache subsides, you might feel fatigued and apathetic. You should see a doctor if headaches start to affect your daily life.

Many people get a headache when they don’t drink enough water. Other common symptoms of dehydration include fatigue and sleepiness.

Dehydration headaches often go away within a few hours after drinking water. To prevent headache and fatigue caused by dehydration, aim for at least 8 to 10 glasses of water a day — more if you’re working out or it’s a particularly hot day.

Headache and fatigue are a common side effect of many different types of medications. Some medications such as diuretics and certain blood pressure medications may lead to headache and fatigue because they can make you dehydrated.

Other medications can interfere with your sleep patterns. Lack of sleep is also associated with headaches.

Caffeine is a central nervous system stimulant. Though it can make you feel alert and reduce fatigue right after you drink it, caffeine can also interfere with your sleep if you consume too much. Poor sleep can lead to fatigue and headache.

If you tend to drink caffeinated beverages on a daily basis, your body becomes dependent on the caffeine. If you decide to eliminate caffeine from your diet, you’ll likely experience withdrawal symptoms, which include both headache and fatigue.

The main symptom of chronic fatigue syndrome (CFS) is severe and disabling fatigue that goes on for at least 4 months and is not improved by rest. Other symptoms include frequent headaches, muscle pain, joint pain, sleep problems, and trouble concentrating.

Fibromyalgia is a chronic disorder that’s associated with widespread pain and general fatigue. The pain usually occurs in tender points, also called trigger points, in many areas of the body.

People with fibromyalgia may also have frequent headaches.

Researchers and doctors don’t know what causes fibromyalgia, but more is learned about the condition every day. If you’re experiencing, pain, headaches, and fatigue that won’t go away, see a doctor for an accurate diagnosis.

Any disorder that affects your sleep, including insomnia, restless leg syndrome, bruxism (grinding your teeth at night), and sleep apnea, can cause headache and fatigue. Sleep disorders are also associated with migraine headaches.

Lack of sleep causes levels of the stress hormone cortisol to rise in the body, which can negatively impact mood. Other symptoms of high cortisol include weight gain, irritability, acne, headache, and fatigue.

A concussion is a temporary brain injury and is usually the result of an injury or impact to the head.

Seek immediate medical attention if you’ve had a head injury and think you could have a concussion. Aside from headache and fatigue, other symptoms of a concussion include:

  • unconsciousness
  • memory problems
  • continual vomiting
  • behavior changes
  • confusion
  • blurred vision

A hangover is a consequence of drinking too much alcohol. Since alcohol has a dehydrating effect on the body, it can cause headaches. Drinking alcohol also causes your blood vessels to widen (vasodilation), which is associated with headaches as well.

Alcohol may also interrupt your sleep, which can leave you feeling drowsy and fatigued the next day.

If you frequently experience headache and fatigue after drinking alcohol, consider these 7 ways to prevent a hangover.

Headache and fatigue are common symptoms of the flu and common cold, which are both caused by viruses. Most of the time, headache and fatigue will be accompanied by other symptoms, such as fever, runny nose, sore throat, and a cough.

Anemia occurs when the number of healthy red blood cells in your body is too low. When this happens, your body’s tissues can’t get enough oxygen. If you have anemia, you’ll likely feel fatigued and weak. You may also feel dizzy and short of breath and have pale skin and brittle nails. Headaches are another common symptom of anemia, particularly anemia caused by iron deficiency.

Hormonal changes both before and during menstruation can lead to both headache and fatigue. Some women experience migraines during menstruation.

Most women have experienced some form of premenstrual syndrome (PMS) right before their period. Common symptoms of PMS include:

  • emotional outbursts
  • sore breasts
  • fatigue
  • headache
  • food cravings
  • changes in sleep patterns

Staring at a computer, tablet, or cell phone screen all day may be necessary for school or work, but it’s incredibly stressful for your eyes. As your eyes become fatigued, you might start to have a headache.

Another symptom of digital eye strain is general fatigue or tiredness. You may also have difficulty concentrating or problems sleeping, which could cause you to become even more fatigued.

To combat eye strain, try to look away from your screen every 20 minutes to something that’s at least 20 feet away, for at least 20 seconds.

Headache and fatigue are just two of the many symptoms of pregnancy. Fatigue is a result of high levels of the hormone progesterone. Likewise, headaches can be caused by hormonal changes and changes in blood volume during pregnancy.

Systemic lupus erythematosus (SLE) or lupus for short, is a chronic autoimmune disease. An autoimmune disease occurs when your immune system mistakenly attacks your own body.

Symptoms of lupus are varied. Common symptoms include:

  • severe fatigue
  • headaches
  • a “butterfly” rash on the cheeks and nose
  • joint pain and swelling
  • hair loss
  • fingers turning white or blue and tingling when cold (Raynaud’s phenomenon)

See a doctor if you’re experience headache and fatigue along with any of the above symptoms. A doctor will have to run several tests to make a diagnosis.

Depression can make you feel emotionally and physically drained. It can also affect your sleep, leading to both headache and fatigue. Other symptoms include severe sadness, social withdrawal, body aches, appetite changes, and feeling worthless.

A doctor or mental health professional can help you find the best treatment for depression so you can start feeling like yourself again.

Anyone who experiences unexplained headaches and fatigue should see a doctor. While some of the causes of these symptoms, like caffeine withdrawals and the common cold, will go away on their own, others require long-term management.

If medications are to blame for your headache and fatigue, you doctor may want to switch you to a different medication or lower your dose.

You’ll also want to visit a doctor right away if your headache is sudden and severe or accompanies a fever, stiff neck, confusion, vomiting, behavior changes, vision changes, numbness, or difficulty speaking.