People who have lung cancer can be drowsy for several reasons. Most are problems that can be life-threatening if left untreated. Therefore, if a patient with lung cancer appears drowsy, it’s very important that she or he be seen by a health care provider as soon as possible.

These are the most common problems that may cause drowsiness in someone with lung cancer:

• Spread of the lung tumor to the brain
  Many cancers can spread to the brain, which may result in decreased alertness. It is common for lung tumors to spread to the brain.
   
• High calcium level in the blood
  Some cancers, such as lung cancers, cause the body to regulate calcium incorrectly, so that the level gradually increases. The symptoms of elevated calcium are usually drowsiness, confusion and constipation.
   
• Abnormal blood sugar levels
  This may have several causes. Diabetes can be a side effect of some medications used to treat cancer, particularly one called dexamethasone. A person may already have diabetes prior to being diagnosed with cancer. Some cancers cause the blood sugar to become lower. Any of these problems can cause decreased alertness.
   
• Other imbalances in the blood
  Low sodium levels can cause drowsiness.
   
• Medications
  Medications such as morphine, or those used for nausea may cause drowsiness.