August Alsina -- Wakes Up From 3-Day Coma ... After Collapsing Off Stage

August Alsina's condition was much more serious than his camp initially let on -- the singer was in a coma for 3 days after fainting on stage in NYC ... but he is finally awake.

August posted a gnarly photo of himself Friday morning after regaining consciousness ... thanking friends and family for their "prayers and concerns." In the pic, his head is heavily bandaged and an oxygen mask is strapped to his face.

TMZ broke the story ... BET's Best New Artist of the Year collapsed and fell off a stage Monday night. The next day, Alsina's rep said he was suffering from seizures and was in ICU.

Alsina's rep now confirms he'd been in a medically induced coma since Tuesday, and on a breathing machine.