Does a person with Parkinson's and Alzheimer's need a specific amount of sleep?

Today was the second day this week that my dad did not know who my mother was. He usually takes a nap every morning and afternoon. On saturdays he sleeps less than other days. He usually goes to bed between 8:30 and 9 pm. I usually go over at 7:30 to help get him up and ready for church. Today he was tired and asked my mom who she was. Is this normal? It is very upsetting to see him this way. Could it be the mix-up in his routine or is this natural progression? Any suggestions on how to help mom and him at the same time would be helpful.