How long an adrenaline rush lasts depends on what causes it. If someone plays a prank on you and jumps out from behind a wall, the adrenaline rush is usually momentary and subsides within minutes.
In crisis situations, an adrenaline rush can last longer, often up to an hour. Once the threat disappears, the parasympathetic nervous system attempts to return the body to its nonarousal state.
If the sympathetic nervous system is continually activated from lasting psychological stress, it may have long-term effects on your immune and inflammatory responses.