Even though I've been checked for Diabetes (and it was negative), I also experience my sugar levels dropping. I don't have the same symptoms as blindhearted does, my hands tend to shake vigourously, and my legs begin to feel weak. The only problem when that happens while driving is that I have to stop for food, or suck down a coke, or some high sugar stuff you'd give to a diabetic having the same reaction.
As for a coughing fit, I don't have a "fit", but I've had a few coughs where I'd see stars! It actually happened while I was driving (fortunately alone--the wife would have freaked!) and I had to focus immediately on the road right after. I'm not going 80 (At least not 80 mph, more like 80 kmh which is about 50mph!), but some cases which that happens is bumber to bumper and mirror to mirror! (It gets so cramped, we nearly touch mirrors on the road!)
I wondered about this, too, but was a bit hesitant to start a spool on it.
Fortunately, I haven't gone so bad to pull over, but it's definitely something to prepare for, if it were to get that bad. (*knock on wood* here, too!)
My problem is, I've got a 5 speed, and if my hands are full, I gotta prevent the window from getting "splattered" as soon as I start coughing!