A Tear In My Eye

This is after Season 6.
After Jay and Nya reuniting, the blue ninja tried to give Nya a necklace that represents their love until a group called Dragon Riders causing the ninja to defeat them. One of the Dragon Riders was aiming for Nya but Jay went in front of her and hit the ground very hard.

Opening his eyes, he doesn't remember who he is or even know anyone. This breaks Nya's heart and the ninja with Skylor and the side characters to find a way to bring his memories back before the Midnight Dance comes up.

The worse condition is that if Jay doesn't get his memories back before midnight on the Midnight Dance, he will lose the true him and will be confused forever.