Sea air was actually shown to be a remedy to various illnesses in the 18th century. But, this was not commonly believed along the entire medical community.

https://books.google.com/books?id=NSHa5u76G08C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

Nervousness was considered a "popular disease" in the late 18th century. Most commonly discussed and found in the middle and elite class. Many people of higher class were said to have bad "nerves" or "nervousness" because there was no clear definition of a nervous disorder at the time.

https://muse.jhu.edu/article/680400