always worried about things - according to macmillan dictionary
filled with deep anxiety, especially about oneself or about the nature of existence
those hard times when you feel nothing at all, your head is filled with dark images and the world seems grey.
you have second thoughts about everything, and you may blame yourself about past mistakes.
you may even start to thing that your birth is a mistake, and you get stuck into nothingness.
Most of Placebo songs are of angst-ridden nature. I love them.