Oh NOOOO!!!

Some naaasty Mexican food got Mercedes is sick, but she CANNOT be sick!

TOMORROW, Glee will grace us with a TWO-hour episode, where everyone swaps character roles. But let us not forget... It's also NATIONALS!!! (You're tuning in to see Lindsay Lohan Perez as a judge, right?

The McKinley kids are going head-to-head with their arch rivals, Vocal Adrenaline, in Chicago. Judging by our exclusive clip, those VA kids did NOT forget to pack their A-game! That means The New Directions cannot be down a player -- especially a their powerhouse!

Something must be done -- and Sue Sylvester has a plan!

Presssss Plaaaaay to hear their plan to keep the group’s chance at winning Nationals alive (above)!!

AAAAND make sure you tune into Fox on Tuesday to see who wins… AND to check out our guest starring Glee debut!