Insomnia One common problem in insomnia is that the bed has become connected with things other than sleep. This makes it hard to use the bed for sleep when you want. Hypersomnia One side effect of cancer and cancer treatment is sleeping too much. This is called hypersomnia, meaning "too much sleep.'' Coping with the Cognitive Effects of Brain Tumors Brain tumors may affect your cognition, which is your ability to think, reason, and remember. Many people with brain tumors have problems with concentration, language skills, and memory, as well.