Demi Lovato Hospitalized After Possible Allergic Reaction, Quickly Discharged

Demi Lovato had a scary start to her week after suffering a possible allergic reaction that landed her in the hospital ... but TMZ has learned she's doing just fine.

Demi gave fans a glimpse of the ordeal on Instagram Monday night, sharing a photo of herself with an IV in her arm and a hospital wristband.

She wrote, "sooooo i'm either allergic to passionfruit or sushi now!"

The singer didn't elaborate on what symptoms she experienced ... and didn't mention any possible triggers other than the passionfruit and sushi.

Sources with direct knowledge tell TMZ ... Demi didn't stay overnight and was discharged shortly after checking in to be evaluated. We're told her symptoms subsided pretty quickly.