A male (84) sometimes sleeps all day.

Many many possibilities here. He needs to see the MD for a complete physical.

Sleep disorders are completely normal with older people. It sounds like he may be a sundowner, where someone sleeps all day and becomes more active at nighttime. If it had just come on suddenly, I would recommend talking to his doctor about it. If it's gradual, that you should still bring it up the doctor because it could be due to an underlying condition, but know that it's completely normal for older people to sleep long hours at a time. I'm the caregiver for my 91 year old Grandmother, and she sometimes sleeps for a solid 3 days, will stay awake for almost 24 hours, and then sleep another 3 days. It's because even just the simple things such as eating becomes a task for them.