Here's the situation:
A (male) friend's dad (call him X, he's in his mid-fifties) usually wakes up in the first two hours after going to bed to do washroom business. Last night, X woke up and realized he forgot essentially the last (few) year or so, such as his son having graduated from university (though he remembers his son is in university, and where), and pretty much all associated events in the last year (and even some other things like how to turn on the computer). He kept asking questions like "What year is it? What day is it? What month is it?" and looking generally confused, but didn't appear to be too absent-minded (like sleepwalking, I'm told). That basically continued for about an hour or so, until he was persuaded to fall back asleep. This morning, X had no recollection of the event, and pretty much had his memory intact (though maybe his wife telling him about the incident made him a little anxious).

My question is, would this be early onset of Alzheimer's? Or regular sleepwalking? Or transient epileptic amnesia? Or something else? How should my friend proceed? This is the first time it's happened (to their knowledge).

Thanks.

Does he take Ambien or a similar drug at night?

What other medications does he use? Statins for cholesterol?

Sometimes people can get stuck in a sleep stage, and be quite impaired. When they get up in the night alot to go to the bathroom etc, they tend to not wake up fully, because then it is difficult to fall back to sleep. So they learn this habit of only partial arousal.
This is when falls and accidents happen too.

If he remembers when fully awake, I don't think it is Alzheimer's.
But you might have him mention this to the doctor incase it is related to other medical issues he might have.

He doesn't take any medication (to my knowledge, he hasn't taken any medications in his entire life, save any medical emergencies I'm not aware of), just home-brewed Chinese herbal soups (but then so does the rest of that family). He also has no history of medical conditions, and none in his family. He went to the doctor just yesterday morning for a regular check up I think so they'll talk to the doc when the results are in.

Thanks for the prompt reply.

It seems that X went out to different stage of sleep. It might be that he was sleepwalking or get into REM phase where he woke up. REM usually starts 2 to 3 hours after falling a sleep.

I think there is nothing you should worry about thus I can't be sure and I don't guarantee that my informations are correctly. The best thing would be obviously to go for professional help to check brain activities.

Cheers