Demotion warning?

After being placed in Silver Division 1 this afternoon i decided to play a few matches,

i won 1, and then lost 2, then lost my last match due to a DC 15 min in (we were doing fairly well as a 4v5, but ultimately lost because of a poor teamfight)

In the lobby i was just told that i had been demoted down a division.

What happened to the grace period? Should i expect this? What if i had just won a BO3 and then lost 2-3 matches, would i STILL get demoted? I feel like riot should better explain the demotion system so that my utter surprise and regret, that i would have to play probably a minimum of 7-8 WINS to get back to silver 1, assuming that i win my first BO3 that i'm given.