Hi Mary,
Since there are any number of reasons why your dad would be experiencing frequent night time urination, the best thing to do would be to consult his doctor. While online sites are great resources for information to be able to ask all the right questions when it's time to see your doctor, but they can not take the place of your doctor's sound medical advice.
You can read about excessive night time urination here. Some of the treatments involved and some of the causes. There is also a good article here by the Harvard medical school that gives some information about Nocturnia.
I hope this helps. Please stay in touch and let us know how you and your dad are doing!
Vicki M
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