Dave East is gonna get REALLY HIGH to get over the Yankees loss -- telling TMZ Sports it's gonna take some good grass to move on from the NY "L."

We got the rapper -- who's a Yanks diehard -- just hours after the Pinstripes fell in the ALDS ... and that's when he revealed the perfect East strategy for how to cope with the defeat.

"Some good weed," he says.

Dave's from New York City ... so the loss reallllly sucks for him -- but he tells us he's still ride-or-die with Aaron Judge and the boys no matter what.

In fact ... the "Perfect" spitter tells us he's rooting for anyone that plays the Sox from now on.

"I'm against the Red Sox, man."

Only 188 more days 'til the 2019 rematch ...