Date: 202005
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Night
Aircraft: Cheetah; Tiger; Traveler AA5 Series
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Cruise
ATC / advisory: Center ZZZ
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Physiological - Other; Situational Awareness
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Illness / Injury; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Tonight was one of the scariest flights I've been a part of. While flying at 11;000 ft. I started to experience what I suspected to be hypoxia. I requested from Center to reduce altitude to 10;000 ft.; which they accepted. I started to feel better initially but the symptoms never subsided; I started to get light headed and my extremities were starting to tingle; I was turned over to [the next] Center and requested if possible another route that would allow me to get to a lower altitude because I suspected that I was experience hypoxia they were able to give me a lower altitude and a vector. Center was amazing at handling my request and was able to get me to a lower altitude and would communicate when the next lower sector was coming. During this time I felt like the symptoms were subsiding but from time to time would come back. There was a point where I was assigned 6500 ft.; Center gave me a low altitude warning; at that time I look at my altimeter and read 6450 ft. and increased my altitude to 6550 ft. I was able to get down to 6000 ft. a couple minutes later and the majority of all symptoms subsided. Once on with Approach they were able to bring me down to 5000 ft. and step me down all the way to my destination without incident. This was my first time experience hypoxia and although at all times I felt I stayed within the tolerances when I landed Approach said Center wanted to talk to me to make sure I was ok. I called the supervisor and thanked them for helping me out in what could have been a horrible situation. Towards the end of the conversation he did mention there was a moment that they were losing radio and radar contact but it appeared that I was outside of tolerance; I explained my situation and that when the warning came out I had 6450 ft. on the altimeter but went ahead and climbed 100 ft. because I knew I was in a low altitude scenario. I'm not sure if it was the lack of radar or a altimeter setting that was wrong on my part. I do recall when Approach gave me altimeter setting I had to ask them to repeat since it was a lot lower that what I was running. I believe I was at 29.98 and [they] gave me 29.78.




Synopsis: AA5B pilot reported receiving a low altitude alert from Center while experiencing symptoms of hypoxia.