In a similar spirit to my previous question, I wonder who was the first artist to feature a nose-bleed when thinking, shall we say, "provocative thoughts"? Did it become popularized in anime/manga because of the popularity of the artist's work or because it is a common belief in japanese folklore?
As Beska notes in useful comments at the related question Does the “bloody nose” trope necessarily imply a sexual situation?,
I think it steps around the question: whether there is a difference between what is understood in normal Japanese society vs anime.
However, when I mentioned this to a Japanese person (someone who was not a big anime viewer), she was confused, and adamant that a bloody nose would normally just mean that the person was excited in general, and it would not necessarily have anything to do with sexual excitement. That's the problem I have. I mean everyone seems to "know" this...I did as well. And yet, when I asked someone Japanese about it (far more likely to know about the cultural norms than me), they had no idea what I was talking about (and were very adamant that it was not the case that it was sexual.)
This seems to be correct: that outside of the subculture of anime and manga, associating nosebleeds with arousal, or portraying it as a visual euphemism of sorts for such, is not common knowledge among the general Japanese population. As such, we can deduct that it does not originate in well-known folklore and thereby became a common belief. It most likely originated in manga or anime. Although the concept has now become recognized enough among otaku that Punchline features it in every episode, I discussed this with a Japanese female college student who is heavily involved in subculture (has manned a booth at Comiket, member of the university's Manga Research Society, practices drawing manga, reads manga and watches 4-koma gag anime, enjoys doujin visual novels, vocaloid fan) and even she had never heard of this trope, since it is not customary to come across it within the genres that she likes. Though by no means conclusive, she said that if you mention that a character gets a nosebleed, the average Japanese person will imagine that the character got punched by someone.
Apparently, NicoNico News interviewed an Ear/Nose/Throat doctor in Yamaguchi prefecture, Dr. Kanaya Kouichiro, on the topic of nosebleeds in anime/manga, but the video is no longer available online. His personal theory as to an origin is sports such as pro wrestling:
In the past, people like pro wrestlers would intentionally give themselves small cuts on their forehead in order to build tension and atmosphere in a match. I can only imagine that the idea of extreme stimulation and an excess of energy was portrayed in the same way with nosebleeds, and it’s come to be the accepted method of representing that feeling.
I have no idea when, or by whom, the nosebleeding started to depicted in Japanese visual arts, but the nosebleeding as a sign of excitement is traditionally held to have developed during the feudal times when men and women (of the upper classes) were supposed to live their lives apart—but of course they needed some way to woo each other! And so, the men, while walking on the other side of the street mentally forced their noses to bleed when they saw someone “hot” being walked along, and the courting could begin on opposite sides of drawn curtains. Some consider this an accurate history while others consider it a myth, probably the truth lies somewhere in between, as usual.
If this is true, then this form of specialised nosebleed might have been depicted in art for quite awhile. But of that I have no knowledge.
An interesting thing, I just realised, is that if this is the true history of the sexually ritualistic nosebleed, then
(a) women had no need to develop such “skills”, and
(b) homosexual men also had no such need.
Thus much of the anime and manga today—especially in the boys’ love scene—are not true to the real history! :P (Male homosexual acts were in these times—again, in the upper classes—something considered pure and good, as females were “worth” less and not something you might not have easy “access” to when you felt certain urges.)