Matt Stafford's wife just went OFF on the NFL over the Lions QB's false-positive COVID-19 test results ... saying the improper diagnosis has made her life a "nightmare" the past few days.

"I have been losing my mind because of how my Family has been treated since my husband was put on COVID-IR," Kelly Stafford said Tuesday.

"Even after we knew it was false positive, our school told us they were not allowed back, I was approached in a grocery store and told I was 'endangering others,' my kids were harassed and kicked off a playground, I was told I needed to wait in my car when trying to pick up food, and people closest to us had to get tested just so they could go back to work .. and that's just to name a few things."

Kelly says she believes it's all the NFL's fault ... saying league officials should have been more sure of Stafford's diagnosis before putting him on Detroit's COVID-IR list.

"Maybe we should be absolutely positive a person has covid before releasing that info to the world," Kelly said. "I'm sharing our experience because I don't want it happening to any other family that plays for this league."

As we previously reported, the Lions said in a statement Tuesday ... Stafford took six tests in the last week, and five were negative with one turning up as a false positive.

The team made it crystal clear -- "Matthew does NOT have COVID-19 and never has had COVID-19 and the test in question was a False-Positive."

The team added, "Also, all of Matthew's family have been tested and everyone is negative."