Metta World Peace -- I Was Hospitalized in China ... I Got Pretty Sick

Metta World Peace had a rough start to his pro basketball career in China -- telling TMZ Sports he got pretty sick right when he got to town ... and spent 3 days in a Chinese hospital.

Metta -- who inked a deal with the Sichuan Blue Whales back in August -- said he fell ill on day 1 of his international career ... and doctors hooked him up with IVs to help him recover.

Peace says the experience was A LOT different from the American hospitals he was used to -- but says the fans were very supportive.