Pass out Definition 1 of 4Pro Tip 1/3Sudden Fatigue Use when someone collapses due to extreme tiredness or other overwhelming conditions. Marathon runners often pass out at the finish line. Pro Tip 2/3Medical Emergencies Indicates a serious health issue, requiring immediate attention. Call an ambulance if someone passes out and doesn't wake up. Pro Tip 3/3Figurative Use Sometimes used humorously to describe extreme reactions to surprising news. I nearly passed out when I saw the price tag.