Yes, it is pretty common to feel light headed during the WHM breahting, it is a form of hyperventilation and you are blowing off a lot of CO2 so you are really creating some wild swings in your blood gasses. The main thing is to take full breaths and not to breath faster than you can breath correctly. You don’t want to take a bunch of quick, shallow breaths as that can drop your oxygen levels faster than you want. It takes some practice to get a feel for it, kind of like the isometrics, but with a little more practice you’ll be more comfortable with it. It is certainly a different feeling than what we are used to but in the end it isn’t bad for you so enjoy the ride.