A C206 PILOT WAS CLEARED FOR FULL STOP BUT FLEW A TOUCH AND GO; CONFLICTING WITH ANOTHER DEPARTING AIRCRAFT.

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I DEPARTED FROM ZZZ TO DO SOME PROFICIENCY FLYING AND WENT TO HWD TO PRACTICE LNDGS. INBOUND TO HWD; I CONTACTED HWD TWR AND REQUESTED TOUCH-AND-GOES. THE TWR CLRED ME TO LAND ON RWY 28L. I THOUGHT THAT I HAD BEEN CLRED FOR THE OPTION. SHORTLY BEFORE I TOUCHED DOWN ON RWY 28L; THE TWR CLRED AN EXTRA FOR A L 270 DEG DEP OFF OF RWY 28R. THE EXTRA BEGAN TKOF SHORTLY JUST AS I TOUCHED DOWN. I RAISED THE FLAPS AND RESET ELEVATOR TRIM TO TAKE OFF AGAIN FOR A CIRCUIT. AS I APPLIED TKOF PWR ON THE ROLL; THE EXTRA WAS ALREADY AIRBORNE AND AHEAD; CLBING RAPIDLY. I REALIZED THAT HE WOULD NEED TO MAKE A L TURN ACROSS MY COURSE JUST AS I BECAME AIRBORNE. AT THAT POINT HWD TWR ASKED ME TO STATE MY INTENTIONS. I REPLIED THAT I WISHED TO MAKE L CLOSED TFC AND WOULD STAY BEHIND AND BELOW THE EXTRA UNTIL HE WAS CLR. I APOLOGIZED AND ASKED IF I HAD MISSED A CALL OR WHETHER I HAD MISUNDERSTOOD THEIR INSTRUCTION. THE CTLR REPLIED THAT I HAD BEEN CLRED TO LAND; NOT FOR THE OPTION. I APOLOGIZED AGAIN AND ASKED HOW I SHOULD PROCEED. THE TWR INSTRUCTED ME TO GO AHEAD AND CONTINUE TO MAKE L TFC. I HAVE MISSED VERY FEW RADIO CALLS IN MY APPROX 20 YRS OF FLYING. I ATTRIBUTE THIS MISTAKE TO: 1) FATIGUE. 2) FAILURE TO PROPERLY EVALUATE MY OWN PHYSICAL/MENTAL CONDITION PRIOR TO INITIATING THE FLT. I WAS RECOVERING FROM A HEAD COLD. I WAS NOT TAKING ANY MEDICATION AND MY SINUSES WERE CLR; BUT I WAS STILL SOMEWHAT FATIGUED FROM LACK OF REST. I WAS EXPECTING TO BE CLRED FOR THE OPTION; SO I FAILED TO RECOGNIZE THAT I HAD BEEN CLRED TO LAND. THE EXTRA'S DEP REQUEST SHOULD HAVE CAUSED ME TO QUESTION WHETHER I WAS CLRED FOR THE OPTION; AND I SHOULD HAVE; IN ANY EVENT; MADE A FULL-STOP TAXI BACK; EVEN IF I BELIEVED THAT I WAS CLRED FOR TOUCH-AND-GOES. I MAKE A PRACTICE OF EVALUATING MY HEALTH FOR FLT DURING THE DRIVE TO THE ARPT AND DURING PREFLT. IN THIS CASE; I DID NOT RECOGNIZE CLUES THAT SHOULD HAVE SHOWN THAT I WAS NOT AS ALERT AND SHARP AS I NEEDED TO BE IN ORDER TO FLY.