Celebrity hairstylist Jesus Guerrero had lost 20 pounds and was complaining of chills and hot flashes leading up to his unexpected death, TMZ has learned.

Sources close to the situation tell TMZ ... Jesus had been feeling sick since September last year but continued with work commitments in Dublin, Ireland, as well as in England, and Dubai, in the United Arab Emirates.

When Jesus got back to the U.S. from Dubai, he was driven to an L.A. hospital on February 21, and died the next day.

We're told there was no history of drug or alcohol use, and an autopsy has been completed ... but toxicology results remain pending.

Jesus' death was described as "sudden and unexpected" by his sister, and several A-List celebs he worked with over the years -- including Kylie Jenner, Jennifer Lopez, and Katy Perry -- posted emotional tributes to their friend.

Kylie herself covered the cost of transporting Jesus' body back to his family in his hometown of Houston, Texas, and announced she’d pay for his funeral.

Jesus was 34.