LIGHT TWIN PILOT REPORTS FALLING ASLEEP AT FL180 ON RETURN LEG OF ALL NIGHT FREIGHT RUN.

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ARRIVED TO WORK AT AROUND XA45 TO COMPLETE A SCHEDULED CARGO FLT. HAD DONE THE SAME RUN FOR NEARLY A YR NOW AND WAS VERY FAMILIAR WITH THE RTE; TIMES; ETC. DEPARTED ZZZ AND ARRIVED IN ZZZ1 WITHOUT ANY ISSUES. USUALLY UPON ARR; I GET A CREW CAR; GO GET SOMETHING TO EAT; AND COME BACK AND SLEEP FOR ABOUT 3 HRS BEFORE I HAVE TO RETURN TO ZZZ. THERE WAS NO CREW CAR AVAILABLE; SO I WENT UPSTAIRS AND SLEPT FOR 3 HRS. WAS WOKE AT AROUND XG00 BY THE DRIVER STATING MY PLANE HAD BEEN LOADED AND WAS READY TO GO. WENT OUT AND RAN A PREFLT; CHKED WX; DID WT AND BAL; AND WAS OFF. FLT WAS FINE UP UNTIL ABOUT VOR. I FELT VERY FATIGUED AND TIRED. GOT A HDOF TO CTR; ONLY IT WAS A FREQ I HAD NEVER USED BEFORE. I COULD HEAR OTHER PLANES BUT NOT THE CTLR. RATHER THAN TAKE THE CHANCE OF STEPPING ON EVERYBODY; I CHOSE TO WAIT IT OUT; HOPING I COULD HEAR HIM/HER BETTER THE FURTHER W I WENT. THAT IS REALLY THE LAST THING I REMEMBER UNTIL I WOKE NEAR ZZZ. THE PLANE HAD A WORKING AUTOPLT AND A GPS THAT I HAD PROGRAMMED FOR THE ARR I WAS ASSIGNED. THE CDI WAS IN GPS MODE AND SLAVED TO THE AUTOPLT. WHEN I WOKE I THINK I WAS 'SOMEWHAT NEAR' WHERE I WAS SUPPOSED TO BE ON THE ARR. THEN I LOOKED AT MY RADIOS AND ALT AND THEN REALIZED I HAD REALLY MESSED UP BY FALLING ASLEEP. I IMMEDIATELY CHANGED THE RADIO TO ZZZ APCH AND HE GAVE ME AN EBOUND HDG AND A CLRNC TO DSND. HE ASKED IF I NEEDED ASSISTANCE. I SAID NO AND LANDED WITHOUT FURTHER ISSUES. I NEVER RECEIVED A PHONE NUMBER TO CALL SO I DIDN'T REALLY KNOW WHAT TO DO. I HAVE NEVER COMPLETED ONE OF THESE FORMS; BUT WAS ADVISED TO DO SO BY OTHER PLTS. I FEEL THAT THIS EVENT HAPPENED DUE TO INADEQUATE SLEEP; INSUFFICIENT NUTRITION; AND COMPLACENCY (BOREDOM). WHILE IN COLLEGE I TOOK CLASSES IN HUMAN FACTORS; AND CRM; BUT READING ABOUT IT AND EXPERIENCING IT ARE 2 ENTIRELY DIFFERENT THINGS. I NOW SEE HOW DANGEROUS FATIGUE REALLY CAN BE; AND THAT IT IS NOT SOMETHING TO TAKE 'LIGHTLY.' TODAY I CHOSE NOT TO DO SOMETHING I HAD PLANNED TO DO WITH FRIENDS; BUT RATHER SLEPT INSTEAD. I FEEL THAT I AM RESTED AND CAN SAFELY FLY HOME WITHOUT ANY REPETITION OF LAST NIGHT'S EVENTS.