I would term what you’re describing as a false connotation, where a person assumes a meaning for an unfamiliar word before its denotation is clear. To be fair, however, a physician who uses a Greek- or Latin-derived term unknown outside the profession should know that a patient would infer a more serious condition than a garden variety nosebleed.
From a writer’s perspective, connotation can enrich — or manipulate — the readers’ understanding of a concept or entire text:
You’ve heard the words denotation and connotation before. Denotation refers to the dictionary definition — it’s a very literal use of the word. Connotation means word choice to convey more than its literal definition. It means using words to imply meaning or even exaggerate meaning. — Edith N. Wagner, Express Yourself: Writing Skills for High School, 2002.
This techniques was used to great effect by Republican strategist Frank Luntz, who before the 2000 US presidential election coined the term death tax to refer to the federal estate or inheritance tax:
The term was used by the Republican Party to support the repeal of the estate tax by creating a false impression of the tax in the mind of the voter. In the U.S. prior to 2001, the estate tax almost exclusively applied to the extremely wealthy with assets totaling upwards of two million dollars. Through careful manipulation, the Republican Party managed to convince almost a fifth of the American electorate that the Estate Tax would apply to them, whereas in reality it affected less than 2% of estates.
From a reader’s perspective, an awareness of connotation may be a learning strategy to understanding unfamiliar vocabulary, but that doesn’t mean it works 100% of the time. A word may be also fettered with a negative connotation that has nothing to do with the word itself. The word niggardly ‘miserly’, for instance, has been steadily decreasing in usage, mostly likely because its first two syllables are identical to a racial epithet.
I personally never use the word bucolic ‘pastoral’ because for the life of me, I can’t associate a word with two back vowels and whose last two syllables are identical to a disease of infants and horses with a beautiful country scene. And don’t even get me started on quotidian.