Another nail in my coffin of realizing how easy it is to lose one's focus, Michigan State University is reporting that even a 3-second distraction is likely to do you in.
Your full citation:
Momentary Interruptions Can Derail the Train of Thought.
Altmann, Erik M.; Trafton, J. Gregory; Hambrick, David Z.
Journal of Experimental Psychology: General, Jan 7 , 2013, No Pagination Specified. doi: 10.1037/a0030986