The major danger on the Autobahn is the huge difference in speed between lanes. If there are only two in your direction, the left will have vehicles traveling 50 to 80 mph faster than the big trucks in the right lane, which are plodding along at 60 miles per hour-slower on hills. Drivers traveling 75 to 100 mph are caught in a no-man's land-too slow for the left lane and much too fast for the right. Imagine this: you are in the right lane cruising at a sensible (for Germany) 140 kph (88 mph). Ahead, just as you round a long curve, is a giant truck going 60 mph in your lane. Your rear view mirror reveals a BMW closing fast in the left lane at say 120 mph. Your choice is to stand on the brakes and pray you don't rear-end the truck, or jump on the accelerator, switch to the left lane, and hope the Beamer doesn't rear-end you. A high level of concentration is required for this sort of driving, particularly if you venture in that 75 to 100 mph no-man's land. A few hours of such driving takes its toll. You will be tired.
Rolling with the Big Boys
If you have a fast car and want to compete with the fliers in the left lane you'll have to be especially alert. Passing a line of traffic going 75 mph when you're hurtling along at 110 mph becomes a major problem rather quickly if someone in that line decides to change lanes in front of you. There might be room on the left shoulder, but that's your only out. Watch every vehicle in the right lane like a hawk for any sign that they have a lane change in mind. (More about the Autobahn.)
In the United States, especially California, one sees stubborn drivers camping in the left lane at precisely 55 mph. Blithely they roll along, secure in the knowledge that they're traveling the speed limit and breaking no laws. Well, in Germany they are breaking the law, and German drivers will quickly deal with them. It is difficult to imagine anyone withstanding the onslaught of flashing lights and tight tailgating that European drivers use to deal with slow left lane drivers. Almost never will they resort to passing in the right lane. Instead, they will ride the slower car's bumper, flash headlights, and even blow the horn. If you're a "left laner" who resists everyone, no matter who wants to pass, you may wish to rethink that practice. German drivers have a way of making nonconformists conform.