i'll tell you how it feels for me when i set a pb (current pb 5:43).
For the first two minutes i have no urge to breathe at all. At first i even feel like my lungs arent all the way full (due to hyperventilation), and slowly they start feeling more and more full, until it snas me out of my daydream, usually at about 2:30 or so. From then on, i feel pressure building up in my chest, starting towards a contraction, and it starts being a little uncomfortable. If i dont resist the contraction urge at all, then i will get a very weak contraction around 2:45-2:50, but i usually resist until i strt getting a suffocating feeling all over me, and then relax and get a solid first contraction at 3:15 or so. Then i just try to relax and find a mental peace, and go with the contractions. They dont really get bad until a bit after 4 minutes, and usually by 4:30 i need to sit up to take the contractions easier, as they are coming faster and harder.(Another thing is i get very very hot at the end of statics, so i always take my shirt off before hand and get my room very cool) At about 5:00 to 5:15, it reaches a 'peak difficulty' for me, where the urge to breathe is the greatest. if i can resist the urge then, i can push to a BO if i want to, because it gets a little easier from then on. i have to stand up unfortunately, i have never been able to do over 5:00 without standing up to take the contractions. I know if i could relax i would have more 02, but the contractions get too strong. At the end of the static, around 5:30-5:45, i sit down and wait for the feeling that im out of oxygen, usually feeling faint or my vision going a little 'off'. then i do a controlled breath out, and a few hook breaths if i felt like i pushed myself a bit too far. Also, right when i breathe out, i feel a ruch of happiness if it was a good static, and i cant stop smiling for a few seconds, its almost overwhelming.
let me know if i skipped anything
rory