Rihanna -- It's a Miracle ... No More Bronchitis!!!

Rihanna certainly bounced back in a big way from her bronchitis just days earlier ... partying it up for her birthday.

The singer posted video of her 28th birthday celebration.

We broke the story, her reps told us Rihanna bailed at the last minute on the Grammys because her doctor warned her that her bronchitis was so bad, if she sang she'd do permanent damage. Others said she just threw a fit during rehearsal because of a seating dispute.