A PIPER WARRIOR PLT ENTERING THE VFR PATTERN AT LWM MISTOOK A BIRD FOR AN ACFT CLOSE BY AND CLBED OUT OF THE PATTERN.

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I WAS TRACKING THE 240 DEG RADIAL TO LWM. I HAD CONTACTED LWM TWR AND HAD RECEIVED INSTRUCTIONS TO LAND ON RWY 32; ENTER R DOWNWIND; MAKE R TFC AND RPT MID FIELD. AS I CROSSED THE VOR AND PREPARED TO MAKE MY TURN TO DOWNWIND; I SAW ON THE L SIDE OF THE AIRPLANE WHAT APPEARED TO BE ANOTHER AIRPLANE (OR SO I THOUGHT). I IMMEDIATELY EXECUTED A R TURN AND STARTED TO CLB OUT OF THE TFC PATTERN; INSTEAD OF THE REQUIRED L TURN. I WAS QUITE FLUSTERED AT THIS POINT; THINKING I HAD JUST AVOIDED A MIDAIR COLLISION. THE TWR THEN ASKED WHAT WAS GOING ON AND WAS I GOING TO LAND. I REPLIED THAT I NEEDED TO CLB (WHAT I MEANT TO SAY WAS THAT I WANTED TO LEAVE THE TFC PATTERN). I HAD GOTTEN MYSELF A LITTLE DISORIENTED. I WAS MOMENTARILY CONFUSED ABOUT WHETHER I WAS LNDG ON RWY 32 OR RWY 23. I QUICKLY GOT MYSELF UNDER CTL AND TOLD THE TWR THAT I WOULD STILL LIKE TO LAND. THE TWR GAVE ME INSTRUCTIONS TO EXECUTE A 180 DEG TURN TO RETURN FOR LNDG ON RWY 32. I DID THIS AND LANDED WITHOUT INCIDENT. ONCE ON THE GND THE TWR ASKED FOR MORE CLARIFICATION AS TO WHAT HAPPENED. I EXPLAINED TO HIM THAT I THOUGHT I SAW OTHER TFC AND THAT STARTLED ME AND FOR A FEW MOMENTS I WAS DISORIENTED. AFTER I THOUGHT ABOUT THIS; WHAT I THINK I SAW WAS MOST LIKELY A HAWK THAT WAS CIRCLING CLOSE TO THE ARPT. WHAT I SAW WAS SOMETHING FLYING VERY CLOSE TO MY PLANE AND IT SENT A CHARGE THROUGH ME. I DISCUSSED THIS WITH MY CFI ONCE I WAS ON THE GND. THE DISORIENTATION ONLY LASTED A FEW SECONDS; BUT I MADE A BAD DECISION IN THAT TIME. A SUDDEN RUSH OF ADRENALIN CAN HAVE; POTENTIALLY; DEVASTATING CONSEQUENCES. I NEED TO MAKE SURE I DON'T LET A SMALL; STARTLING DISTR CREATE A BIGGER PROB.