Date: 202007
Local time of day: 0601-1200
Flight conditions: Mixed
Weather elements / visibility: Clouds Building; 10
Light: Daylight
Aircraft: Skylane 182/RG Turbo Skylane/RG
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Initial Approach
Reporter organization: Personal
Reporter function: Pilot Flying; Captain; Single Pilot
Reporter qualification: Flight Crew Private; Flight Crew Instrument
Human factors: Communication Breakdown; Physiological - Other
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Illness / Injury
Contributing factors: Environment - Non Weather Related
Primary problem: Environment - Non Weather Related

Narrative: A brush with hypoxia? A [senior] healthy pilot; on a flight from ZZZ to ZZZ1 at 10;000; just above the cloud tops on a very warm day; was contacted by Air Traffic for a simple route change during the last 45 minutes of the flight. After three tries by Air Traffic I was unable to repeat back change but was somehow able to program the change into the autopilot. I then connected the dots and requested lower to 6000. I was clearly having symptoms of hypoxia. A look back at the outside temperature during that flight was 15°C at 10;000 for a density altitude of 12;000 plus and I had been there almost 5 hours. I do have some additional thoughts... First; after three tries to copy the route change Air Traffic basically gave up trying to get me to read back correctly the routing change. After several minutes... I did get the two waypoints route change in the autopilot; but was unable to give Air Traffic a successful read back. Second; when I requested lower because I had connected the dots with possible hypoxia; Air Traffic required me to request lower three times. Each time saying; 'Please repeat your request Aircraft X; please repeat request;' which I understood to be a little hazing for my earlier inability to copy the routing change... Or maybe I was actually mumbling the request? And thought I was speaking clearly?Third. Maybe the Controller; hearing my inability to read back correctly; maybe because of unclear speech on my part… should have connected the dots? That I; the Pilot; may have symptoms of hypoxia; or other medical issues; and addressed that with me? Lastly. After descending to 6;000; I made a mistake by not informing the Controller that I may have had a case of hypoxia or another medical problem. It would have been a learning experience for both of us. I'm correcting that now.Additionally; prior to this at approximately 4 hours into the flight; I had an overwhelming desire to take a nap. I knew I was well rested; fed and hydrated before the flight. Aircraft X is equipped with CO2 detectors. I knew it was probably not that. I opened the vents which appeared to help. The aircraft was on autopilot for the entire trip; so Traffic Control only saw a nice flight on their scopes; and I was only tasked with monitoring engine temperatures. I own both flight oxygen and an oximeter. But both were on loan to a relative who was having heart issues and were not in the aircraft at the time.




Synopsis: C-182T Pilot Flying reported a possible encounter with hypoxia.