We lose an hour of sleep when Daylight Saving Time (DST) begins, which happens at 2 a.m. on the second Sunday in March in most places that observe it. At this time, clocks are set forward by one hour ("spring forward"), causing the loss of one hour of sleep that night. For example, in 2025, this will occur on Sunday, March 9th at 2 a.m., when clocks jump forward to 3 a.m. This shift often leads to sleep disruption and health impacts due to the sudden change in circadian rhythm and sleep schedule.