That happened to me once.
When I was living in the dorms at Framingham State College in the late 1990's, I had an atomic clock/alarm radio. It must have been a particularly stressful semester but I was having a difficult time falling asleep and staying asleep.
I remember one night, I woke up in the middle of the night, the clock read the appropriate time (I can't remember the exact details) ... somewhere around 2 in the morning. But the date month, day, and year were off by a couple of decades: reading sometime in the late 1960's.
I assumed it was some kind of solar flare or solar wind that might have inadvertently tweaked the atomic clock radio signal. The clock fixed itself sometime the next day.