Cough

[Cranky Old Man]

At somewhat random moments throughout the day, I'll suddenly break into continuous coughing fits of over a minute long at a time because of acquiring an intense and unbearable itch in my throat. The feeling is rather bizarre: it's like someone is sticking a feather down my throat and tickling it, and no amount of coughing helps to stop the itch. However, in the instant of coughing, I can have momentary relief. So really, the only reason why I cough for a minute straight is because the itch is there for a minute, and then disappears. To prove my hypothesis that coughing does not stop the itch at all, I once went a minute straight without coughing when that itch appeared, and it indeed subsided once the minute was over. That minute was so unbearable I had tears flowing down my eyes.

The itch tends of appear when I'm on the verge of falling asleep in a moving vehicle, but not when I fall asleep in bed. Does this happen to anyone else?

Would that happen to be the SAME moving vehicle?
I could link you to an online symptom checker, but it's pretty obvious that the vehicle that you are refering to has also transported an animal like a dog, or a chemical (or seat cleaner) or asbestos, that you are having an allergic reaction to. It could be that your drowsiness is part of that reaction too - that your throat not only itches, but also swells, so that you don't get enough air.