I believe Michael's reaction was due to the drapes being open. I'm sure that, due ot his position, he ran his house rigidly, and that included "small" things like the drapes being closed at a certain time. I also feel that his hitting the deck was because he saw the gunmen; otherwise, he would have hit the deck sooner - like immediatley upon seeing the open drapes.
"The only wealth in this world is children. More than all the money and power on Earth." --Michael Corleone
