Small Transport
Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 75; Flight Crew Total 4500; Flight Crew Type 1500
Fatigue; Situational Awareness
No Specific Anomaly Occurred All Types
General None Reported / Taken
Company Policy; Human Factors
About 1.5 hours into my flight at FL230; and into my descent; I started feeling an urge to sleep.  I was amusing myself texting and communicating and flying but nonetheless; I started to feel very; very tired.  Prior to the flight; I felt fine.  I think I slept my usual 7 hours of sleep the night before.  I moved my COVID-19 face mask aside and drank some water.  That helped a little bit.  But upon putting the face mask back on my face; the feeling came back and I caught myself drifting.  Then I realized...it was my COVID-19 MASK!  I removed the mask and felt fine the rest of the flight.  I didn't have a pulse oxymeter handy but I wish I did.  I think I was inhaling CO2 instead of oxygen.  COVID strikes again!
Pilot reported feeling sleepy while flying and suspected that it was the COVID-19 mask that was causing the problem. The pilot removed the mask and felt fine afterward.