In book 2 of Galen’s De crisibus, Galen describes a crisis as “a sudden change in a disease, either towards death or recovery; which last is produced by nature secreting the good from the bad humours, and preparing the latter for excretion.” In what ways might the bad humours be excreted?
This answer we can find in book 3 of De crisibus.
“It is the peculiar property of burning fevers to be terminated by an eruption of blood from the nose, or some other part of the body; or by a profuse, universal, and warm sweat breaking out after a rigor; or by a bilious vomiting, or some other excretion of the humours.”
The good news is that if you get a bloody nose during a fever (and a decongestant isn’t the likely culprit), you could be on your way to recovery. The bad news is that you could also be on your way to death, but at least the bad humours will be gone.
Translations from Alpinus, Prosper. The Presages of Life and Death in Diseases. Translated by R. James. London, 1746.