Cough

[Cranky Old Man]

Nope, I've gotten this itch from being in both my car as well as any bus. It just always happens when I'm near falling asleep.

It's important to know whether you are falling asleep due to natural causes, like not having slept enough at night, or if your sudden drowsiness always occurs together with the rash, because in that case, you're falling asleep due to respiratory problems - the rash could be occuring deep in your lungs as well.

Anyway, "I see you have a cough"...
http://www.everydayhealth.com/symptom-ch...port/cough

Edit: Also, the transportation may vary, but when you start to feel the rash, look outside your car/bus window. Is the car/bus passing the same location? Is it next to an industrial area?