Narrative:

After departing at XA32; I established a climb at 500 FPM to an altitude of 6500 ft MSL. I contacted approach for flight following. Upon reaching 6500 ft MSL; I was seeing scattered clouds and decided to descend back to 4500 ft MSL. I maintained 6500 ft for about 5 mins before deciding to descend. I descended to 4500 ft MSL at a rate of 500-700 FPM. I was established at 4500 ft MSL south of ZZZ and crossed ZZZ at XA59. I continued at this altitude for at least another 15 NM. Approach notified me of aircraft inbound to their airport. I confirmed visual contact of 4 aircraft inbound. They were all no factor. At this time I felt fully alert and fine. At about 15 NM north of ZZZ and while outside of the class B airspace; I began to feel what I thought was raindrops on the backs of my hands. This confused me a bit and I felt for something wet; but it was not wet. This sensation continued and progressively increased up my right arm and in my feet. I also noticed my head felt foggy and my breathing became more rapid. I asked my passenger how he felt; and he confirmed the same symptoms. We had just turned the heat full on 2 mins earlier. I immediately shut off the heat and opened all the vents. Because the onset of this sensation developed so rapidly; I did not want to wait and see if it worsened or progressed any further. I called approach and told them I would like to come in for a landing as I was feeling funny. I requested vectors to land. They brought me in with vectors. I safely landed the aircraft. I was greeted with paramedics. I felt fine at this time; still a little fuzzy-headed; but now a little nervous about all the attention. I did not declare an emergency landing and I did not expect all the attention. While coming in; ATC asked me to clarify my condition; and I told them I felt pinpricks in my hands and feet and a little fuzzy-headed. I believe I experienced hypoxia. It confuses me though that it affected both myself (a non smoker) and my passenger (a smoker) at exactly the same time. Also; I'm surprised at the occurrence at this altitude when we were not at 6500 ft MSL for more than 5 mins and established at 4500 ft MSL for over 10 mins before experiencing the symptoms. But; all the symptoms point to hypoxia. I believe I made the right decision to make a precautionary landing. To avoid this situation in the future; I will go with an instructor to high altitude and acclimate myself to high altitude flight. The aircraft was inspected for a carbon monoxide leak; but none was found.

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Original NASA ASRS Text

Title: C172 PILOT REPORTS STRANGE TINGLING SENSATIONS WHILE VFR AT 4500 FT; AND ELECTS TO LAND IMMEDIATELY FEARING HYPOXIA.

Narrative: AFTER DEPARTING AT XA32; I ESTABLISHED A CLB AT 500 FPM TO AN ALT OF 6500 FT MSL. I CONTACTED APCH FOR FLT FOLLOWING. UPON REACHING 6500 FT MSL; I WAS SEEING SCATTERED CLOUDS AND DECIDED TO DSND BACK TO 4500 FT MSL. I MAINTAINED 6500 FT FOR ABOUT 5 MINS BEFORE DECIDING TO DSND. I DSNDED TO 4500 FT MSL AT A RATE OF 500-700 FPM. I WAS ESTABLISHED AT 4500 FT MSL S OF ZZZ AND CROSSED ZZZ AT XA59. I CONTINUED AT THIS ALT FOR AT LEAST ANOTHER 15 NM. APCH NOTIFIED ME OF ACFT INBOUND TO THEIR ARPT. I CONFIRMED VISUAL CONTACT OF 4 ACFT INBOUND. THEY WERE ALL NO FACTOR. AT THIS TIME I FELT FULLY ALERT AND FINE. AT ABOUT 15 NM N OF ZZZ AND WHILE OUTSIDE OF THE CLASS B AIRSPACE; I BEGAN TO FEEL WHAT I THOUGHT WAS RAINDROPS ON THE BACKS OF MY HANDS. THIS CONFUSED ME A BIT AND I FELT FOR SOMETHING WET; BUT IT WAS NOT WET. THIS SENSATION CONTINUED AND PROGRESSIVELY INCREASED UP MY R ARM AND IN MY FEET. I ALSO NOTICED MY HEAD FELT FOGGY AND MY BREATHING BECAME MORE RAPID. I ASKED MY PAX HOW HE FELT; AND HE CONFIRMED THE SAME SYMPTOMS. WE HAD JUST TURNED THE HEAT FULL ON 2 MINS EARLIER. I IMMEDIATELY SHUT OFF THE HEAT AND OPENED ALL THE VENTS. BECAUSE THE ONSET OF THIS SENSATION DEVELOPED SO RAPIDLY; I DID NOT WANT TO WAIT AND SEE IF IT WORSENED OR PROGRESSED ANY FURTHER. I CALLED APCH AND TOLD THEM I WOULD LIKE TO COME IN FOR A LNDG AS I WAS FEELING FUNNY. I REQUESTED VECTORS TO LAND. THEY BROUGHT ME IN WITH VECTORS. I SAFELY LANDED THE ACFT. I WAS GREETED WITH PARAMEDICS. I FELT FINE AT THIS TIME; STILL A LITTLE FUZZY-HEADED; BUT NOW A LITTLE NERVOUS ABOUT ALL THE ATTN. I DID NOT DECLARE AN EMER LNDG AND I DID NOT EXPECT ALL THE ATTN. WHILE COMING IN; ATC ASKED ME TO CLARIFY MY CONDITION; AND I TOLD THEM I FELT PINPRICKS IN MY HANDS AND FEET AND A LITTLE FUZZY-HEADED. I BELIEVE I EXPERIENCED HYPOXIA. IT CONFUSES ME THOUGH THAT IT AFFECTED BOTH MYSELF (A NON SMOKER) AND MY PAX (A SMOKER) AT EXACTLY THE SAME TIME. ALSO; I'M SURPRISED AT THE OCCURRENCE AT THIS ALT WHEN WE WERE NOT AT 6500 FT MSL FOR MORE THAN 5 MINS AND ESTABLISHED AT 4500 FT MSL FOR OVER 10 MINS BEFORE EXPERIENCING THE SYMPTOMS. BUT; ALL THE SYMPTOMS POINT TO HYPOXIA. I BELIEVE I MADE THE RIGHT DECISION TO MAKE A PRECAUTIONARY LNDG. TO AVOID THIS SITUATION IN THE FUTURE; I WILL GO WITH AN INSTRUCTOR TO HIGH ALT AND ACCLIMATE MYSELF TO HIGH ALT FLT. THE ACFT WAS INSPECTED FOR A CARBON MONOXIDE LEAK; BUT NONE WAS FOUND.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.