Surprised at how fast MMR can swing - is this normal?

So I was going up in mmr by the looks of who I was being matched against in normals - high silver. Starting to see some golds. I was increasing my winrate by one tricking shyvana mostly with 65%ish winrate.

Then I decide to spend a week or two trying out new champions, testing new builds and strategies, and generally just messing around for fun. Losing a majority of the games.

Then I noticed I was being paired against bronzes of varying degrees. So I hop back on old reliable Talon, and try to play serious again, and I've been crushing the past 20 games or so with almost 80% winrate. Even winning with teemo. Mind you, several of these loses were outright someone leaving our team so its 4vs5.

It seems like dropping MMR to crush games would be a good strategy for chest farming.

I might see an occasional silver now. But still bronzes. How long do I have to keep crushing these games before MMR raises me up to mid/high silver again? It's kind of annoying at this point because I dont find this level of play enjoyable. It narrows the spectrum of what I can viably play and win, forcing me to pick hard carry snowballers to overcome my team.