The coughing and blacking out due to anxiety was actually really interesting. We were in her head the whole chapter, and there were a lot of hints that it was getting to her. She constantly talked about how nervous she was, and once she started having the acute symptoms of anxiety she admitted she was afraid.
I like that we see why, too. That she had it, somewhere in the back of her mind, that when they finally had sex this was all going to be over. The thought physically scared her, to the point that she had symptoms. It's a really interesting character moment. We've heard her be confused over how excited and nervous she's been before, and could guess at why she felt that way, but now its established. She likes the feelings she's having, she wants to connect sexually, but she's scared that once she does she'll lose this relationship like she always has in the past.
It's as sweet as the rest of the manga has been, too, with the chapter ending with them hugging each other in bed after having a good time just hanging out and enjoying each others company. Honestly, this thing's adorable.