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Everyone's seen the clips ... and the memes of the time sports talk radio legend Mike Francesa fell asleep on the air.

Now, Mike is explaining how the hell it happened ... and it's actually a pretty solid excuse.

We got Francesa out at a falafel truck in NYC when he told us the backstory of that one fateful moment with Yankees reporter Sweeny Murti back in 2012.

Mike also weighed in on his beloved NY Yankees -- and told us why it would be a huge mistake to sleep on Aaron Judge.