History records that Marie Antoinette's hair suddenly turned white overnight after hearing she would be sent to the guillotine. If this is really true, then what is the MOST likely explanation?

See the explanation of canities subita below

Explanation:

Marie Antoinette's experience is now termed as Marie Antoinette syndrome.

There is an occurrence of Marie Antoinette syndrome when a huge shock or life-threatening situation result in people losing the color of their hair.

But the stories behind Marie Antoinette syndrome is regraded as a historical fiction. The reason is that canities subita is the only condition that can make hair to turn to white. Canities subita explains that the hair can only turn white gradually but not overnight.

Therefore, MOST likely explanation that may make hair to seem that it has turned white overnight under canities subita is when there are already strands of different colors like white, grey and black; and there is a sudden massive fall out of the black and grey hair, the white-colored hair will be the only ones  that will remain. This will give the impression that the hair has changed to black overnight.

I wish you the best.

how is this health related