i have done 2-3 rounds of Wim Hof's hyperventilating, after 30 deep breathes, he says to just stop and breathe in when you feel you need to (probably didnt breathe for 60-90 seconds due to such saturation, he then directs you to hold this breathe and squeeze your brain for 10-15 seconds.
stupidly i did this for what must have been 30-50 seconds and have had a bad headache since, i did it last night and 24 hours later i still have the same pain which actually feels like it is slightly towards the front but more central (which is where all the blood supply is) i also have been a bit dizzy/unbalanced this morning but have run 5k this evening.
reading on the internet you obviously stumble upon some very worrying potentials, i do not want to go to the ER for a headache and look stupid, i am going to leave it 24 more hours and if the same pain exists, i will begin to worry and will no longer doubt i have caused a serious issue and will have no qualms about visiting, especially since i dont suffer with head aches.
so this is a word of warning against that I suppose, and also some documentation for my family in case I die, although I am not sure they will ever see this post :D.