Sleeping Problems: Hypersomnia or Somnolence Syndrome or Nightmares

Approved by the Cancer.Net Editorial Board, 03/2012

People living with cancer may experience sleeping problems related to the cancer, cancer treatment, emotional factors, or other unrelated medical conditions. Sleeping problems may include hypersomnia, somnolence syndrome, or nightmares. Learn more about insomnia–€”another sleeping disorder.


Hypersomnia (also called somnolence, excessive daytime sleepiness, or prolonged drowsiness) is a condition with which you may feel very sleepy during the day or want to sleep for longer than normal at night. It can include long periods of sleep (10 or more hours at a time), excessive amounts of deep sleep, and difficulty staying awake during the day. In addition, daytime napping typically does not relieve the excessive sleepiness.

Hypersomnia may interfere with your relationships, prevent you from enjoying activities, and make it difficult to handle daily activities, such as attending doctors' appointments, completing household chores, and managing family or work responsibilities.

Although similar, hypersomnia and fatigue are not the same. Fatigue involves feelings of exhaustion and lack of energy that are not relieved by sleep. However, unlike hypersomnia, fatigue is not associated with excessive daytime sleeping and the inability to stay awake.


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

  • Cancers of the brain and central nervous system (CNS)
  • A secondary brain tumor (cancer that has spread to the brain from somewhere else in the body)
  • Chemotherapy, such as teniposide (Vumon), pegaspargase (Oncaspar), and thalidomide (Thalomid)
  • Other prescription and over-the-counter medications, including some antidepressants, antinausea medications, opioid pain killers (pain medications), sedatives (medications that calm or cause sleep), antihistamines (medications used to treat allergy or cold symptoms), and sleeping pills
  • Anemia (low red blood cell count)
  • Changes in hormone levels in the body
  • Other symptoms of cancer or side effects of cancer treatments, including hypercalcemia (high levels of calcium), hypokalemia (low levels of potassium), hypothyroidism (a condition in which the thyroid gland is underactive and doesn't make enough thyroid hormones), and depression


Relieving side effects–€”also called symptom management, palliative care, or supportive care—is an important part of cancer care and treatment. Talk with your health care team about any symptoms you experience, including any new symptoms or a change in symptoms.

If possible, hypersomnia is first treated by diagnosing and treating the underlying cause. Often, hypersomnia related to chemotherapy improves after treatment ends. If other medications are causing it, your doctor may be able to substitute a different medication or adjust the dosage. Your doctor may also prescribe stimulant medications to help you stay awake during the day.

The following behavioral strategies 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.
  • Engage in enjoyable activities that require your full attention, such as spending time with friends, writing letters, or playing with a pet.
  • 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 foods that make you sleepy and heavy meals during the day.
  • Avoid alcohol and caffeine.

Somnolence syndrome

Somnolence syndrome is a type of hypersomnia associated with cranial radiation (radiation therapy to the head) in children. Symptoms of somnolence syndrome include excessive drowsiness, prolonged periods of sleep (up to 20 hours a day), headaches, low-grade fever, loss of appetite, nausea, vomiting, and irritability. Symptoms usually occur three to 12 weeks after the end of radiation treatment and can last a few days or several weeks.


Nightmares are vivid, frightening dreams that usually cause the person to wake up able to 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.

Nightmares are often associated with an increase in emotional stress, and they are thought to be a way in which the mind works through unresolved feelings and fears. Sometimes, nightmares are caused by certain medications (such as some antibiotics, iron supplements, opioid pain medications and heart medications), withdrawal from CNS depressants (substances that can slow brain function, such as alcohol, opioids, and some anti-anxiety medications), and uncontrolled pain.

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, discussing 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 the content or themes of the nightmares, such as writing in a journal or drawing a picture.
  • Make up alternative endings or storylines to the nightmares, and visualize them.

Remember that nightmares are not real, and they do not predict the future or cause bad things to happen. If the nightmares become frequent or continue for a prolonged time, cause excessive anxiety, or prevent you from sleeping well, talk with your doctor or seek help from a counselor.

More Information

Managing Side Effects


Strategies for a Better Night's Sleep

Additional Resources

Oncology Nursing Society: The Cancer Journey: Sleep Disturbances

National Institute of Neurological Disorders and Stroke: Hypersomnia