The toxic phase of Yellow Fever usually begins after a brief period of apparent recovery (often 1–2 days after initial symptoms) and is marked by high fever, jaundice (yellowing of eyes/skin), severe abdominal pain, persistent vomiting (sometimes blood), bleeding from gums or nose, dark urine, confusion or delirium, shock, and rapidly worsening liver and kidney failure; once this phase starts, the illness can become life-threatening within hours to a few days, with a high risk of bleeding, organ failure, and death, which is why immediate hospitalization and ICU-level supportive care are critical.