The Lag In My Reflection

I sat in my bed after waking up, not wanting to budge or get ready. All I had wanted to do was lay In bed and get an hour or more of sleep. But I had to get ready and time doesn't slow down for anyone. I stood up and yawned tiredly. Standing, I got in my school uniform and went to the bathroom to brush my teeth like every morning. I got my green toothbrush with stars on it and started to brush my teeth.
While I was brushing my teeth I started to see a lag in my actions, as if my movements were too quick for the mirror. I stared at my reflection and stopped brushing for a second. Confused, I moved my arm up and when I did, my reflection didn't copy...
My reflection just stood there with huge eyes engulfing the light around it. The reflection couldn't copy every move, even if it tried, but that's not me. I fell back a bit startled, but stood up again quickly. I made more movements and it copied once more, but it was lagged, as if the things I was doing had been pulled back a bit in time.
"What are you.?" I asked my reflection, but it gave me no response. It just stared back at me. It was as if that wasn't me, like my own reflection isn't me.
I knew I've noticed something wrong with me for months, I just figured it was nothing. But what had just happened isn't normal.. None of the other times were like this, it had only ever been a tiny lag.
It then stopped mimicking me and began to smile, grinning ear to ear.

"I"
"Am"
"You."