The fear of slave revolts in the American colonies/states probably didn’t amount to much until after Haiti. Haiti being the near genocide of French whites and mulattos. But that wasn’t until 1791.
There had been the Stono Rebellion of 1739 in South Carolina but I doubt that the Continental Congress had that in mind.
The Nat Turner rebellion didn’t happen until 1831. That one left the lasting fear of a Haiti style revolt.
I think John Brown's raid scared the bejezus out of them. I think it contributed greatly to the belief that the two sides needed to separate.