Flex 5v5 Dropped an Entire Divsion? What's Up With That?

Hello there Emomiime here. So as lots of eager summoners did, whenever preseason first came out I was very excited to start ranking up in flex que. I played my 10 games won 7 lost 3 and ended up in Silver IV. Riot then told me I needed to play another game in order to be placed yet a second time. After playing the gaming and happen to lose it, I dropped from Silver IV to Bronzed III?!?!?!? What the heck is up with that? Why did I need to be placed a second time in the first place and why was the effect so dramatic? I don't understand why this happened to me and how 1 game can effect my rating so much.