The origin of today - April Fools or All Fools Day - is not really clear. There is speculation that the origins is related to when France changed from the Julian calendar to the Gregorian calendar which moved the New Year to January 1, from around April 1 at the spring equinox.
What ever the history may be, today until noon, it is recommended to use caution with your environment, what you hear or read. GOOD LUCK!
You can read more on how this evolved to pranks at these sources:
https://www.history.com/topics/holidays/april-fools-day
https://www.history.com/this-day-in-history/april-fools-tradition-popularized
https://www.britannica.com/topic/April-Fools-Day