EE WAS REPAIRING A MUDBELT & BECAME OVERHEATED. HE RESTED, THEN WORKED THE REST OF THE DAY AT A LESS STRENUOUS JOB. HE WORKED THE FOLLOWING WEEK IN A/C EQUIPMENT BUT CONTINUED TO SUFFER HEADAC HE & FATIGUE. HE SAW DOCTOR MONDAY, 7/22 & WENT IN FOR TESTS 7/23. AFTERNOON OF 7/23 HE QUIT FOR ANOTHER JOB.