On the 20th of September 2019, Friday, then Finance Minister Nirmala Sitharaman announced the change in Corporate Tax rate out of nowhere. No Hints, No Clues, just come and make an announcement.
The Nifty closed 5.32% higher on that day. VIX didn't rise much and was stable between 15 and 15.5
The next day Nifty went up higher again by 2.8%
If you were a leveraged option seller without any hedges, or stop loss, you're wiped out for sure on that day.