Narrative:

I departed ZZZ out to the north practice area; outside the class C airspace for routine training maneuvers in a cessna 172. The sky's were clear and full VMC. During the maneuvers I began to get airsick after I pulled open the cabin heat system. After some time of using the cabin heat I closed the system and continued my training maneuvers thinking the airsickness would go away since it has never been a problem. During my maneuvers I began to get cold again so I opened the cabin heat again and continued more maneuvers. I continued to get airsick. During this period; I think about 30 minutes into the flight; I thought I smelled exhaust so I immediately opened the overhead cabin vents; opened the window and closed cabin heat. I still felt alert so I did not consider myself impaired; just nauseated. I picked up the ZZZ ATIS then contacted approach to return to ZZZ. Approach instructed me to stay in the practice area due to traffic. I continued circling in the area waiting for approach to allow me to return. I think by this time I had been flying for about an hour; not sure. I believe I was flying around 3000 feet. I continued to circle; but eventually started calling approach to see if I could return because I wasn't feeling any better; but felt worse. I am not sure if I was missing their radio calls.I eventually received permission to return on a heading of 150. I turned to 150 and entered the class C airspace. Approximately 5 miles from the field I was informed I would be performing a box pattern to allow traffic to land ZZZ. Approach or tower (I can't remember) gave me a left turn to 100. I remember immediately turning to the right thinking this would be more direct. I realized I was confused and asked the controller to verify a left turn to 100 is really what they wanted me to do. They confirmed the instructions so I made a left turn to 100 thinking this would be a complete 360 turn to 100 from my current heading of 150. When I came to 100 I realized I was confused and this is when I realized I may be impaired due to co poisoning. ATC came back and asked be to make a left turn to 360 which I did and I believe I did acknowledge the instruction. Some time after turning north I remember hearing ATC asking me if I copied their last transmission; which I realized I must have missed their call. I responded by stating that I did not hear their transmission and that I was getting confused with their instructions and that I believe I was suffering from co poisoning. I believe I asked them to get me back to the airport as soon as they could.ATC gave me an immediate clearance to land runway 28. I was able to turn the plane to 28 although I was very tired by this time. During the final visual approach I noticed I was a little slow in responding to airspeed and power changes; but I was able to land the plane and taxi off the runway. I met the fire trucks and sat on the taxi way for a while catching my breath. I told ATC I thought I could taxi the plane to parking. After parking the plane; emts met me at the plane. I did not realize how impaired I was until the emt's asked me some questions. I remember the emt asking me my name and I could not immediately tell him. He then asked me how many quarters are in a dollar. I could not remember and I had to take some time to figure out the answer. I am writing this to inform of my experiencing and what I remember during the events and also to inform that I was able to land the aircraft without an accident. After initial treatment by the airport emt's I was transported to the hospital via ambulance.

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Original NASA ASRS Text

Title: C-172 Pilot reported executing an emergency landing due to Carbon Monoxide poisoning.

Narrative: I departed ZZZ out to the North Practice area; outside the Class C airspace for routine training maneuvers in a Cessna 172. The sky's were clear and full VMC. During the maneuvers I began to get airsick after I pulled open the cabin heat system. After some time of using the cabin heat I closed the system and continued my training maneuvers thinking the airsickness would go away since it has never been a problem. During my maneuvers I began to get cold again so I opened the cabin heat again and continued more maneuvers. I continued to get airsick. During this period; I think about 30 minutes into the flight; I thought I smelled exhaust so I immediately opened the overhead cabin vents; opened the window and closed cabin heat. I still felt alert so I did not consider myself impaired; just nauseated. I picked up the ZZZ ATIS then contacted approach to return to ZZZ. Approach instructed me to stay in the practice area due to traffic. I continued circling in the area waiting for Approach to allow me to return. I think by this time I had been flying for about an hour; not sure. I believe I was flying around 3000 feet. I continued to circle; but eventually started calling Approach to see if I could return because I wasn't feeling any better; but felt worse. I am not sure if I was missing their radio calls.I eventually received permission to return on a heading of 150. I turned to 150 and entered the Class C airspace. Approximately 5 miles from the field I was informed I would be performing a box pattern to allow traffic to land ZZZ. Approach or Tower (I can't remember) gave me a left turn to 100. I remember immediately turning to the right thinking this would be more direct. I realized I was confused and asked the controller to verify a left turn to 100 is really what they wanted me to do. They confirmed the instructions so I made a left turn to 100 thinking this would be a complete 360 turn to 100 from my current heading of 150. When I came to 100 I realized I was confused and this is when I realized I may be impaired due to CO poisoning. ATC came back and asked be to make a left turn to 360 which I did and I believe I did acknowledge the instruction. Some time after turning north I remember hearing ATC asking me if I copied their last transmission; which I realized I must have missed their call. I responded by stating that I did not hear their transmission and that I was getting confused with their instructions and that I believe I was suffering from CO poisoning. I believe I asked them to get me back to the airport as soon as they could.ATC gave me an immediate clearance to land runway 28. I was able to turn the plane to 28 although I was very tired by this time. During the final visual approach I noticed I was a little slow in responding to airspeed and power changes; but I was able to land the plane and taxi off the runway. I met the fire trucks and sat on the taxi way for a while catching my breath. I told ATC I thought I could taxi the plane to parking. After parking the plane; EMTs met me at the plane. I did not realize how impaired I was until the EMT's asked me some questions. I remember the EMT asking me my name and I could not immediately tell him. He then asked me how many quarters are in a dollar. I could not remember and I had to take some time to figure out the answer. I am writing this to inform of my experiencing and what I remember during the events and also to inform that I was able to land the aircraft without an accident. After initial treatment by the airport EMT's I was transported to the hospital via ambulance.

Data retrieved from NASA's ASRS site 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.