This is a story I just heard from my older brother, and I'm not sure if it's true or not…
It happened when he was in college, about ten years ago. There was a close-knit group of about ten people in his major.
After summer vacation ended, everyone was back to attending classes, complaining about the heat and fatigue, and a week had passed. My brother was eating an ice cream in his boarding room at night when he suddenly thought, "Wait, what happened to [Name]?"
When he thought about it, he realized he hadn't seen [Name], a member of their close group, even once since summer break. They were good enough friends to have gone to the beach together over the vacation, so if the guy hadn't shown his face, my brother should have at least called him to check on him. Yet for some reason, he had completely forgotten all about him.
He immediately tried calling, but got voicemail.
The next day at university, he asked the others, "Hey, I wonder what happened to [Name]?"
Everyone started making a commotion, saying, "Now that you mention it, I completely forgot he existed!"
In the end, no matter who he asked, everyone had forgotten about [Name]'s existence until that very day. Since [Name] didn't show up that day either, my brother called his parents' house on behalf of the group, but was told he wasn't there.
He apparently found out later that even the professor who took attendance every time had somehow forgotten to call [Name]'s name.
Two days later, [Name] was found wandering aimlessly on a mountain road in the neighboring town.
According to him, "I got lost in the mountains and kept walking for a whole day and night."
When they checked the date, he said, "Today is [such and such date], right?"—naming a date ten days in the past.
It was chalked up to temporary memory confusion; he was admitted to a regular hospital and was able to discharge soon after, but he himself apparently remained unsatisfied with that explanation.
Among my brother and his friends, it's talked about to this day as a definite case of being "spirits away."
By the way, there's no doubt he actually went hiking in the mountains ten days prior, but the only food he brought with him was a single rice ball…
That wouldn't have been enough, would it?