Janice Dickinson HOSPITALIZED -- After Drug Store Accident in Beverly Hills

Janice Dickinson had a painful run-in with a metal bar yesterday ... when a closing parking garage door struck her in the head so hard, she needed to be hospitalized, TMZ has learned.

It all went down outside the Rite Aid drug store in Beverly Hills ... when Janice was walking underneath the gate and had a collision with the crossbar.

Janice says she was knocked to the ground ... and sustained damage to her knee ... but she tried to go on with her day without medical attention.

But later that night, Janice says the pain began to set in ... and she couldn't sleep. So first thing Friday morning, she went to UCLA medical center ... where doctors ran tests and determined she suffered a pretty gnarly concussion.

Janice is now recovering at home ... but says she still feels "pretty horrible."