I personally experienced this during a job crisis some years ago when it appeared I was about to get canned. I managed to cling to my job by the skin of my teeth, but after about a month my beard, which up to then was fairly dark in color, had turned almost as white as snow. However, this did not happen overnight and neither did the whiskers fall out. Strangely, the hair on my head was unaffected. I finally shaved the beard off so I could continue to look my age.
Welcome to the boards, Tokyo-John.
Cecil Adams column on whether this happens. It notes that this belief has been around for centuries, but often based on rumor or second-hand info:
Maybe something like this happened with you, though you didn’t lose hair, so who knows?
I’ll add an anecdote I’ve heard, without opinion on whether it’s true or not. The story goes that during the U.S. Civil War, many a person in the South had their hair turn white, supposedly overnight. But then again, the South was under a naval blockade that kept many goods from getting through. Some of the white hairs might not have been the result of fright, but rather the inability to get the hair dye they had been previously using.
FWIW, I’ll give a story from my father, WW2 pacific theater combat vet. A lifelong friend of his was on the invasion of Okinawa, and infiltrated the night before the full invasion took place. Said that this caused his hair to go white.
I met the friend when he was maybe 40, and certainly at that point he was both bald and had white hair.