THE PLT REPORTED THAT BEFORE THE FLT, HE HAD TAKEN 2 SOMINEX TABLETS, BUT HAD INSOMNIA & COULD NOT SLEEP, EVEN THOUGH HE WAS VERY TIRED. HE STATED THAT AFTER TAKEOFF, HE THOUGHT HE WAS HEADING SOUTHEAST, BUT LATER, HE FOUND OUT THAT HE WAS GOING NORTHEAST. THE PLT STATED THAT THE ENG STARTED TO SPUTTER & BACKFIRE SO HE LANDED IN A COW PASTURE. DURING THE LANDING, THE ACFT STRUCK A 3-WIRE, BARBED WIRE FENCE. AFTER LANDING, HE RAN UP THE ENG SEVERAL TIMES & IT OPERATED NORMALLY, SO HE ASSUMED THERE WAS A FUEL BLOCKAGE THAT HAD PASSED. REPORTEDLY, HE CHECKED THE ACFT FOR DAMAGE & THOUGHT IT WAS AIRWORTHY. SO HE TOOK OFF & RETURNED TO THE DEPARTURE ARPT. AFTER ARRIVING, HE INADVERTENTLY LANDED ON A PARALLEL TAXIWAY BESIDE RWY 18L. ON THE APCH, THE TOWER TRANSMITTED A WARNING OF THE SITUATION & INSTRUCTED THE PLT TO GO AROUND. THE PLT STATED HE DID NOT HEAR THE TRANSMISSION. WITNESSES REPORTED THE ODOR OF BEER IN THE ACFT & FOUND THE CARPET WAS WET WITH BEER. THE ACFT HAD BEEN DAMAGED DURING THE OFF ARPT LANDING.