the light head and tingeling in the fingers is a a sensation we are looking for and even try to intense those feelings with our breath. But sometimes you dont get it which is nothing to be concered of.

Wim said to leave out the head for the first times you take your cold shower. You can also take a bucket of ice and just dip your hands and feet into it for a couple of minutes.

Always listen to your body, he knows.

Dont do the breathing alone in the water. It can be intense and people passed out. (this is not bad or harmful and very rare) but if you practise in a pool etc there is a risk of drowning .