Demi Lovato Hospitalized

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!"