An Aneurysm was a medical condition that could affect Humans. They were known to occur sudden in people who might have looked just fine shortly before. They were treatable, but might take a person out of commission for some time and require a sufferer to take it easy for a few days after. (DS9: "Inter Arma Enim Silent Leges")
In 2372, The Doctor searched for an aneurysm as one of several potential explanations for his captain's hallucinations. (VOY: "Persistence of Vision")
In 2375, Admiral William Ross was found slumped over his desk while aboard the USS Bellerophon while in orbit of Romulus for a conference. An aneurysm was suspected, and later confirmed. He made a full recovery. Julian Bashir later suggested to the admiral that the aneurysm was set in scene. (DS9: "Inter Arma Enim Silent Leges")