u/IAmBorked

My teacher keeps telling me my timing is sloppy, that I slow down in difficult passages and breeze quickly through easy ones, so I should practice more with the metronome. But here's the thing: it doesn't matter how slow I set it, as soon as I hear that tick-tick-tick, my brain forgets the notes and the fingerings. Where before I could play the right notes, both hands, once it's ticking I struggle with just one hand. What is that about? It's as if my brain has run out of things it can do at once, and paying attention to the beat is just one thing too many.

Thoughts, suggestions?