I remember cycling home after school, met one of the flatmates (housemate actually) halfway, totally in panic, his mum had just called him to tell about a serious terrorist attack and made him go buy candles (in case power went down).
Came home, turned on the TV and watched the towers go down. Spent the rest of the day behind the TV.
Seeing the images again, ten years later, strikes me even more than it did then.