Lindsay Lohan was rushed to the emergency room in NYC last night ... and sources connected to the actress tell us she's suffering from a bad lung infection.
Lindsay has been telling friend she's been dealing with a bad case of "walking pneumonia" for the last couple weeks -- and last night, we're told things got so bad she had to go to the hospital.
We're told Lindsay was taken to Mt. Sinai, where she received medication for the infection -- including antibiotics -- and was discharged shortly after.
Lindsay's currently resting back in her hotel room.