system
Given the following post, respond as if you're commenting on Reddit:
human
[spoilers] X-Men: DoFP - Wolverine.

So, his mind is sent in time to 197X. There, he begins to drown, and his next memory is in 20XX.

But he wakes up in the school, where he is apparently the history teacher. So he had a whole life between being fished out of the Potomac and 'waking up' in Xavier's school. What happened to the Wolverine who was the history teacher? I mean, he's *dead*! All his memories are gone, overwritten by a stranger's from another timeline.

Professor seems awful happy to see a friend he only met in 197X, and seems to not shed a single tear for the man he's known for the past thirty years.
gpt
Xavier didn't lose anyone.  
Logan had pretty strong amnesia as a result of the Weapon X program, it's likely he forgot 197x and 20xx as a part of this process. So an amnesiac is discovered in Canada matching the description of Xavier's friend that had recently been kidnapped. The X-Men mobilize and bring him in and after who knows how many weeks or years of telepathic therapy with the Professor Logan's pre-197x memories return.  

Logan's brain is all sorts of weird because of his time travel shenanigans and ridiculously long life. This is probably just the first of hopefully many more breakthroughs in his therapy.