Harry's patronus shattered when he saw Hermione's state. He was emotionally incapable of casting it.

Forgive me if others have mentioned this idea, or if there is firm evidence that it isn't possible, but..

I've been thinking about this since early on. I know most people feel that Quirrel is Voldemort, but I keep wondering if he's a future, middle-aged Harry from an alternate timeline (but (probably) not the canon timeline). I wonder if Harry destroyed the his universe as prophecied trying to save Hermione, and then time traveled to make another attempt. However, this would cause a paradox, but there is a theory that time travel paradoxes can be avoided if one also switches travels to another universe.

There are a number of things that make me think this, including:

1) "I don't suppose," said Harry, "that it's possible to actually swap people into alternate universes? Like, this isn't our own Rita Skeeter, or they temporarily sent her somewhere else?"

"If that was possible," Professor Quirrell said, his voice rather dry, "would I still be here? "

EY later tells us to pay attention to when Quirrell answered without answering. The implication is, "It is possible, and that's why I'm here."

2) At some point Quirrell is quite surprised when Harry explains how he thinks, or says that he wouldn't lie about something serious, as if it differs from his own memory of his way of thinking as child Harry.

3) There's the trope that time travelers can't touch their past selves without disastrous consequences (the sense of doom, and effects of their magics interacting).

4) Your examples above.

Unfortunately, I have to run, but I have some more examples and will post soon, unless someone shoots this out of the water.

EDIT:

And this is, at least, his second possession, the first being the Weasley brother who thought the rat was Pettigrew? That would have been when future Harry realised he wasn't in his own timeline any longer.