Sleeping Problems: Hypersomnia, Somnolence Syndrome, and Nightmares

Approved by the Cancer.Net Editorial Board, 08/2018

Cancer and its treatment may cause the following sleeping problems:

  • Hypersomnia

  • Somnolence syndrome

  • Nightmares

  • Insomnia, which is discussed in a separate article

Other factors may also cause these sleeping problems, such as emotional concerns or medical conditions unrelated to cancer.

Managing side effects is an important part of cancer care and treatment. This is called palliative care or supportive care. Talk with your health care team about managing or coping with sleeping problems.


People with hypersomnia feel very sleepy during the day or want to sleep for longer than normal at night. Hypersomnia may also be called somnolence, excessive daytime sleepiness, or prolonged drowsiness.

Signs of hypersomnia

The signs of hypersomnia can include:

  • Sleeping for 10 or more hours at a time

  • Excessive amounts of deep sleep

  • Trouble staying awake during the day

  • Excessive sleepiness that is not reduced by taking a nap

Hypersomnia may interfere with your relationships and make it hard for you to enjoy activities. It can also make handling daily activities and family and work responsibilities a challenge.

Hypersomnia and fatigue are similar but not the same. Fatigue is a feeling of exhaustion and lack of energy not relieved by sleep. Excessive daytime sleeping and being unable to stay awake are not signs of fatigue.

Causes of hypersomnia

The following types of cancer, cancer treatment, and other medical conditions can cause hypersomnia:

  • Brain and central nervous system (CNS) tumors

  • A cancer that has spread to the brain from somewhere else in the body

  • Some types of chemotherapy

  • Other prescription and over-the-counter medications, such as:

    • Some antidepressants

    • Medications to manage nausea

    • Some pain medications

    • Sedatives, which are medications that calm or cause sleep

    • Antihistamines, which are medications used to treat allergy or cold symptoms

    • Sleeping pills

  • Anemia or low numbers of red blood cells

  • Changes in hormone levels in the body

  • Other symptoms of cancer or side effects of cancer treatments, such as:

    • Hypercalcemia or high calcium levels

    • Hypokalemia or low levels of potassium

    • Hypothyroidism, which is when the thyroid gland does not make enough thyroid hormones

    • Depression

Managing hypersomnia

To treat hypersomnia, your doctor first needs to find and treat the cause. Treating the cause of hypersomnia, if one can be found, is the most effective way to relieve the symptoms. For example, hypersomnia related to chemotherapy usually improves after treatment ends. If other medications are causing the hypersomnia, your doctor may be able to change the medication or adjust the dose. Your doctor may also prescribe stimulant medications to help you stay awake during the day.

The following behavioral changes may help you manage hypersomnia:

  • Sleep a few hours longer at night to avoid excessive sleepiness during the day

  • Exercise daily in the morning or early afternoon, if possible

  • Do enjoyable activities that require your full attention

  • Try to go to sleep and wake up at the same time every day

  • Get out of bed and stay out of bed until bedtime

  • Avoid heavy meals and foods that make you sleepy during the day

  • Avoid alcohol and caffeine

Somnolence syndrome

Somnolence syndrome is a type of hypersomnia in children. It is linked to receiving radiation therapy to the head.

Symptoms of somnolence syndrome

The symptoms of somnolence syndrome usually occur 3 to 12 weeks after radiation therapy treatment ends. It can last a few days or several weeks. The symptoms include:

  • Excessive drowsiness

  • Sleeping up to 20 hours a day

  • Headaches

  • Low-grade fever

  • Loss of appetite

  • Nausea and vomiting

  • Irritability


Nightmares are vivid, frightening dreams. They usually cause the person to wake up and remember part or most of the dream.

Most people have nightmares from time to time. But the frequency or vividness of nightmares can increase after a cancer diagnosis and during cancer treatment. Frequent nightmares can lead to a fear of going to sleep, restless sleep, and daytime sleepiness.

Causes of nightmares

An increase in emotional stress is a common cause of nightmares. They may be a way in which the mind works through unresolved feelings and fears.

Other causes of nightmares may include:

  • Antibiotics

  • Iron supplements

  • Pain medications

  • Heart medications

  • Withdrawal from alcohol, pain medications, and some anti-anxiety medications

  • Unrelieved pain

Coping with nightmares

Because having cancer is frightening and stressful, it is normal to experience some nightmares during treatment and recovery. The following tips may help you cope with nightmares:

  • Be honest about your fears and feelings. Discuss them with a family member or friend early in the day, rather than at night.

  • Talk about the nightmares with a family member or friend.

  • Find creative ways to express what happens in your nightmares, such as writing about them or drawing pictures.

  • Make up different endings or storylines to the nightmares, and visualize them.

Remember that nightmares are not real. They do not predict the future or cause bad things to happen. Talk with your health care team or a trained counselor if the nightmares:

  • Become more frequent or continue for a while

  • Cause excessive anxiety

  • Prevent you from sleeping well

Related Resources

8 Steps to a Restful Night's Sleep