How about just taking a few advils with just a sip of water? That way you're head ache will go away and you can still do your flush? Or you know what works great for my headaches? Sounds really weird but if you grasp your hair as close to the root as possible and squeeze it, it really seems to help relieve the pressure of the headache, to me atleast. All I know is when I am ready to do a flush and I have to postpone it for some reason, that sucks!! Good luck with your flush and try to stick it out tonight! You'll be glad tomorrow :)