1.In the paragraph, I find a weird expression "the guy" for yourself. I know even in Korean literary expressions, we find "writing style in the first person- omniscient viewpoint ". You treat yourself as an objective person other than you to make dramatic effects, but I barealy have seen this expression in English except the below, so I'd like to confirm if this is the case.

"....John was as famous for his tennis skills as he was for his fits of temper on the court. One afternoon, I was playing an important singles match against John. When things didn't go his way, he began to go downhill, complaning about the game, screaming at himself , and slamming his racket. It looked like, he was having a public nervous breakdown. In the end, the guy who didn't "deserve to be on the same court" with him won in three tought sets. After the match, John announced his retirement from tennis at the age of twenty seven. He explained, "When I start losing to players like him, I've got to reconsider what I'm doing even playing this game." If he thought I'd be insulted, he was wrong. In fact, I loved it....."

2. "go downhill" means a comparison to "losing your self-control or something". right?

3. In the participle phrase, do you think complaining, screaming, slamming are simultaneous actions as go downhill, or consecutive actions following "go downhill"? It's kind of confusing.