Why are option premiums unusually high this week?

I've noticed that premiums have been much higher than usual this past week. For instance, last Friday, the Nifty 23400 CE was trading around 18k, whereas it typically hovered around 6-7k. I understand that the lot size increased from 25 to 75 back in November, but I didn't see premiums spike like this at that time. Am I overlooking something here?