Im unsure, I watched a program one time of those deep sea divers who can hold their breathe for up to 5 minutes. They said after the first need for air the discomforting feeling mellows out. Its like a big hill, once your over the top and on the way down, its a breeze.
holding your breath is different.....
and whne you fall into icy water you gasp for breath jus as a reflex...and then you breath in water and your lungs fill with water..and you drown.....