Cardi B was losing it watching her man Stefon Diggs hit the end zone for a pivotal touchdown ... and her reaction says it all.
Cardi posted a video from bed Sunday, filming her reaction as her boyfriend hauled in a clutch 4th-down pass in the New England Patriots vs Tampa Bay Buccaneers game ... giving the Pats a 14-10 lead.
Check out the video ... Cardi is quite literally lost for words, then starts chanting "bring it home!