Amnesia

Suddenly, it all came rushing back to her! Everything about her, back in her mind! The sonic rainboom, the Wonderbolts, the Element of Loyalty! Even the bookcase incident a week ago! It was all back!
Rainbow Dash flew over to Fluttershy and landed next to her. She was about to speak when Fluttershy gave her a big hug.

"I remember you now!" Said Fluttershy to Rainbow Dash

Rainbow Dash went silent for a moment and then yelled "Yeeaaahhh!!! Woohoo!!!"

She jumped up and flew around her house, still ecstatic with joy. She then landed next to Fluttershy again and gave her a hug back.

Fluttershy then said to Rainbow Dash "You're my best friend."
Rainbow Dash smiled, then whispered back: "You're my best friend too."

After all, Friendship is Magic.