Could Fatigue, Dizziness And Slurred Speech Be A Result Of Lack Of Sleep?

I have a friend that is 86 years old and is having some physical complaints that I believe are related to not getting enough sleep. (I worked as a geriatric nurse for 14 years) He is in good physical health and recently retired. I noticed after his retirement he seemed to be getting thinner and more forgetful. He often goes to sleep at midnight or after and gets up at 5am, reads the paper and has some breakfast and goes back to bed. He gets back up around 11am and doesn't eat until around 2pm. He never lies down to rest in the mid to late afternoon. He has had multiple complalnts of dizziness, slurred speech, and fatigue. I keep telling him he needs to go to bed earlier if he is going to get up at 5am. When I talk to him in the evening around 8 he sounds really tired. He has gone to a multitude of different doctors, had every test imaginable, and they can't figure out what is wrong with him. I don't think they are getting an accurate picture of his lifestyle and how that may be the cause of his complaints. Do you think I may be correct in my belief?