At approximately, 01.35 hrs., During running 13 3/8” casing, drilling crew had difficulty to run the casing joint due to down hole restriction. Crew decided to wash down casing joint using circulating head and managed to run 4 joints successfully till they reached last joint to be run when circulating head suddenly disconnected causing swivel joint, circulating hose and circulating head to drop from top of casing joint to rig floor landing near the rotary table towards the V Door.