You are misunderstanding it. Don’t worry though, yours is a common misunderstanding! So common, in fact, that the Wikipedia article on arousal starts with, “not to be confused with sexual arousal”.
In psychology, “arousal” is a technical term and not all arousal causes harm. In fact, many forms of arousal are quite healthy. Being awake, for example, is a type of arousal and most people stay awake for 16+ hours per day without issue.
Now, you are correct that sexual arousal is a type of arousal, but the type of arousal being discussed in the paper is a very different, very specific type of arousal. This type of arousal is distinct from sexual arousal and the terms cannot be used interchangeably.
Got it and thanks for clarifying. I also amended my last comment since I had a bit of extra time to read the study more thoroughly. I’d be quite interested to see which way the causation goes. Although I suspect that hyperstable arousal may be a symptom of depression rather than a cause of depression, I have heard that the intense adrenaline rush of skydiving may alleviate depression for some people. To me this suggests there may be a way to break out of that hyperstable arousal state by intentionally reaching a state of extremely high arousal, perhaps ending a bout of depression early.