Two possibilities occur to me:
-
Winning games makes your MMR higher, which means you're in harder games with more skilled people. If you win games without improving, your odds of losing go up and up. You are bound to rubberband back to the MMR you belong in.
-
You did improve, you deserved to rise up toward the top of Silver IV, and then had 3 bad unlucky games. Fuck it. It's 3 games. You'll do better in your next games, especially now that your MMR is a little lower and the games will be easier to win.
I should note that it is very very easy to fall into the trap of thinking you're great when you and your team have a great game. When your team is doing well, it's very easy to have a spectacular KDA. I just watched someone on stream last night go like 24/5 as mid Darius in Bronze III. He felt like the king of the world. I had to take him down a peg by pointing out that everyone on his team won their lane, the enemy supp had no Sightstone, and the enemy jungler was 0/14 and chose not to upgrade his basic machete. He did great, but it doesn't mean he's ready for Diamond. He did great mostly because his team did great and the other team did terrible. The same might have happened to you; you might have felt like "I'm much better now, I'm done with Silver, I'm going to have nothing but wins from now on" just because you had some games where your whole team happened to do really well.