It is the feeling of seasonal depression when the days start getting short and nights start coming sooner. "Skamm" means short, "degi" is day, "thung" is heavy and "lyndi" means mood.
Until December 22, when the days start growing again, the occurrence of Short-Day-Heavy-Mood will be on the increase. In fact, we might well blame everything on it, as it seems to affect everyone to some extent. Get in a fight at the office? Skammdegisthunglyndi. Trouble at home? Skammdegisthunglyndi. Late to pay your electricity bill? Skammdegisthunglyndi.
Or just absent mindedness.
To some extent, we can blame the short days for the pandemic H1N1/09 virus (this is the official name, I found out, because "H1N1" is just the regular flu). One of the ways to avoid infection, apparently, is to get plenty of vitamin D. Since we get most of our vitamin D from sunlight, the short winter days are working against us. It is both unhealthy AND depressing.
For the global financial crisis, each day of depressed trading is even more depressing when you look out of the window at three in the afternoon and see only blackness. Employees, called into the manager's office for explanations might claim Skammdegisthunglyndi for their bad results. Managers, on the other hand, strolling around the office may mistake the darkness for the end of the day and just leave. Skammdegis-ljós-lyndi?
"Ljós" means "light." I think I have just made this word up.
There is clearly much more to be said about this - to correlate productivity to the occurrence of Skammdegisthunglyndi, calculate the number of domestic squabbles, filibusters in parliament, and general grumpiness of the people in the days of darkness. Sadly, however, it is just after two in the afternoon and I should be going to sleep now.