I don't know what it is, but it seems like I can never fall asleep on the last night of vacation before I have to go back to work. I went to bed around 9:30pm last night, but ended up tossing and turning until almost 1am. Getting up at 3:30am means it's going to be a LONG day.
I have the opening scene of the rifleman in recorded in a loop and simply try counting the shots he fires from his rifle!