Your score has gone down because we have now added the scores of this game to the overall Brain Score and category scores. Before that, the scores you had didn't count: we were still analysing the performance of our users before the scores went live.
This means that now all of the scores you have ever secured in this game will now be counted towards your Peak Brain Score and your category scores.
This is why your overall score and performance has dropped a bit. Now the category score and Brain Score score are divided between more games. But don't worry, this will happen for all users and as you keep playing, you'll see them go back up!