Justin Timberlake's "SexyBack" TOTALLY works as a five-part harmony.

I may or may not have had a full-fledged panic attack over watching Justin Timberlake NAIL his "Pusher Love Girl" performance on "Late Night With Jimmy Fallon," and I may have had ANOTHER after streaming The 20/20 Experience. Now I'm BASICALLY DEAD after watching Justin Timberlake SLAY his performance of "SexyBack" on "Fallon" with...wait for it...a barbershop quartet! Throw in my love of a cappella (judge me, I DON'T CARE), and I'm a goner.

Watch Justin Timberlake perform "SexyBack" with a barbershop quartet after the jump.

As part of Justin Timberweek (our favorite holiday after Hanukkah), Justin is scheduled to perform every evening this week on "Late Night With Jimmy Fallon." While he's totally rocking out with regular-style performances (check out his rendition of "Mirrors"), JT also seems open to reworking the classics from his catalog. Who knew that meant singing "SexyBack" in a five-part harmony?? Pop stars these days! And where there's a barbershop quartet, there are coordinated striped blazers and MATCHING HATS. Good lord, the hats. Yeah, call me in a month when I've officially regained consciousness.

+ Watch Justin Timberlake perform "SexyBack" with a barbershop quartet.

Photo credit: NBC