What "the thing" refer to in this context

Question

“You've got to take the rest of your potion. Harry,” Mrs. Weasley said at last. Her hand nudged the sack of gold on his bedside cabinet as she reached for the bottle and the goblet. “You have a good long sleep. Try and think about something else for a while…think about what you're going to buy with your winnings!”

“I don't want that gold,” said Harry in an expressionless voice. “You have it. Anyone can have it. I shouldn't have won it. It should've been Cedric's.”

The thing against which he had been fighting on and off ever since he had come out of the maze was threatening to overpower him. He could feel a burning, prickling feeling in the inner corners of his eyes. He blinked and stared up at the ceiling.

_{Harry Potter and the Goblet of Fire}

The sentence looks a bit complicated to me. I think the main part is: The thing was threatening to overpower him. But I'm lost here about what "the thing" really is in this context. Any thoughts on that?

Answer 1

The thing in context is Harry's pain, grief, fear, and stress. He's feeling afraid and overwhelmed, but he's trying to keep these emotions from overpowering him so that he can remain functional.

This is less of a language issue than it is a stylistic choice. The author uses the vague term the thing against which he had been fighting to show that the character doesn't want to admit to these feelings, even to himself. He doesn't want to acknowledge that he's hurt and afraid, so the author 'talks around' the point.

Answer 2

the thing = "that which" or "what"

[What] he had been fighting on and off ... was threatening to overpower him

It is just a placeholder.

The thing I like most about summer is the weather.

What I like most about autumn is the trees changing color.