Hi,
How is your dad? Are there other symptoms present? Chronic insomnia is more common in the elderly and can be caused by psychiatric disorders, such as conditioned insomnia, alcohol and substance abuse, depression and anxiety, chronic pain, nocturia, and many medical disorders such as congestive heart failure, hyperthyroidism, rheumatologic diseases, dementia, Parkinson's disease, chronic obstructive pulmonary disease (COPD), asthma, and gastroesophageal reflux disease (GERD). It is best that further evaluation be done and the cause of the insomnia should be identified and treated. A referral to a sleep specialist may also be indicated. Take care and best regards.
That is not a rare disease. Insomnia and day time sleeping are very common in the elderly. Also, you need to define what "problems's sleeping" means. Do you mean sleeps too much, sleeps to little, snores, awakes, stops breathing, etc.