Corey Feldman was rushed to a Los Angeles hospital after suffering a medical emergency ... TMZ has learned.

Sources familiar with the situation tell TMZ ... Corey was arriving on a flight into LAX from Chicago on Monday afternoon when he was met by paramedics at the gate.

A source close to the former child star tells TMZ ... Corey was feeling very sick on the flight and he was checked out by a doctor who was on board. We're told the doctors think the issue might be pancreatitis or gallstones.

The Los Angeles Fire Department tells TMZ ... they responded to the airport for a patient experiencing a medical emergency. The spokeswoman says the patient, a 54 year old male, was transported to a local hospital for further evaluation and treatment.

TMZ can confirm that man is Corey, who is still undergoing tests at the hospital.

Before the medical emergency, Corey appeared to be enjoying his time in the Midwest ... sharing content from the "Stand By Me" Live Tour in Chicago and posting about a visit to Michael Jackson's family home in Gary, Indiana.

We've reached out to Corey ... so far, no word back.