I have done this for years and used to ascribe it to that "after lunch" thingie, or boredom, and etc etc. Its pretty dangerous when driving!
I would describe it as what a narcoleptic attack would be like: and overpowering urge to close your eyes and sleep right now. It can happen 5 min after I get up or never in a given day. It always begins with yawns and progresses to intense yawning, watering eyes and sinus, and total inability to think straight.
But I've solved it now. It seems like symptoms of oxy deprivation to me, now. But I simply have to stand up and in 5 minutes I'm ok. Don't have to jump about or anything, just remain vertical. Or lie down and sleep, ofc. Yep, it only happens when seated. So now I think it its circulatory in some fashion.View Thread