Have you spent a day busily procrastinating by playing tetris, gone to bed and dreamed of playing tetris? If so you might just have the faint echo of a mental affliction that German people suffered just after World War I. It's called "zero stroke."
Imagine that you're compelled to engage in a certain repetitive mental activity. Even when you're not actively forced to make a certain calculation, you're always, always thinking about it. How would that eventually affect you? If you answered, "negatively," you're beginning to understand what happened to the people of Germany just after World War I. The economy was in ruins, and inflation was climbing so fast that the cost of a loaf of bread was measured first in thousands of marks, then millions, and then billions.
There was no way to keep up with the rising cost of living, but people were forced to try. That meant that they had to multiply millions to pay for the basics of a meal. It meant that, even when they weren't actively calculating, they had to plan – figuring out the value of what they had, and extrapolating what it would buy them tomorrow, and the next day, and the next. This frantic mental activity that never ended left many people with a condition called "zero stroke."
Sufferers of "zero stroke," dreamt of calculating numbers. When they were awake they would constantly write strings of zeros, or strings of numbers, or try to make complex calculations. The inflation made it into their head and they couldn't stop thinking in large numbers, telling people that they had millions of children or were billions of years old. Mentally, they were trying to work their way out of a tough situation with obsessive calculation – literally.
Image: Dave Dugdale