Just days after being hospitalized, former actress Tara Reid was back on the party scene Monday, smoking cigs and hitting up nightclubs in St. Tropez.

TMZ broke the story ... Reid was hospitalized last week in Nice, France for what we were initially told was acute pancreatitis, a bad inflammation of the pancreas that can result in vomiting, nausea, diarrhea and fever.

On Sunday, the 36-year-old tweeted that she actually had food poisoning and hurt her back on a jet ski.

Whatever the ailment -- it's obvious, she's feeling a lot better now.