What happened in placements???

During Christmas time, I climbed from silver 4 to Gold V.

In placements, first two matches were fun, both teams were good, and close matches. I won the first game and lost the second.

Immediatly, I'm paired with people who play ranked for the first time, or play xin support and feeds, troll, play alone in their own lane dying again and again, or just doesn't seem to understand what's going on.

Now I'm back in the world of Bronze I ;_; How did a single defeat, following a victory, throw me immediately so low in matchmaking? :(