New Laser Sailor Has A Question.

Hey everyone. I was out sailing my Laser for the second time today. It was windy, 15-18. I fell off onto a downwind course and eased the main. I went to raise the daggerboard and dropped the sheet. The main ran all the way out and almost instantly I deathrolled to windward. I was just wondering what causes a deathroll. Was it only because I dropped the sheet?

By the way, I was reaching back and forth today absolutely flying. The boat "humming" right along. What an awesome boat.

Thanks!