Nonsense, this is almost certainly not a medical condition, this is normal biology. The constant attention required when driving makes everyone tired, during long drives especially, and if you're tired when you start driving from sleep deprivation or stress it's even worse. The important thing is that you recognize when you're tired and choose not to drive at those times. People get tired and need to sleep, usually, we can recognize it ourselves, it would be nice if technology could help us keep tabs on our tiredness automatically.
I pushed my own tiredness limits when working 40 hours a week at a job 40 miles away while going to college full time that was 20 miles away, when driving for my first job delivering equipment 3 hours away, spending all day at programming the equipment, and driving back home in a single 15+ hour day, and also when trying to commute to work after staying up most of the night with my infant. I've never fallen asleep at the wheel, but I've noticed many times that I'm struggling to concentrate, so I opened a window and found somewhere to pull over and take a walk. Being tired in those conditions is not a medical problem.
Being unsafe, however, is a choice. If and when you get too tired, you ought to pull over into a rest stop (that's what they're there for) and take a quick nap. The trouble is that whether or not you're getting tired is something you have to actively be checking (along with a million other things while driving), it's all too easy to let your brain transfer speed, lane centering, and navigation to your subconscious and not realize where you've been for the last 10 minutes.
If cruise control can help you keep your speed, adaptive cruise can do it while in traffic, lane control can help you check that, and a driver-facing camera can help you check for attention, that's a big help.
BTW I now work about 35 hours a week and commute just under 4 minutes each way - I worked hard to get here, but it's so worth it.