No, 4.2 is not dangerously high. Some people have a prescribed range of 3.0 to 4.0. An INR of 4.2 is barely higher than that and is probably within the margin of error for 4.0. The only way you would be likely to have any real problems from an INR of 4.2 is if some other unfortunate event were to happen at the same time, like if you were to fall and hit your head, and you started bleeding inside your skull, then the INR of 4.2 could be a problem. Except for some kind of unlucky coincidence like that, an INR of 4.2 is no big deal. The nick that you got while shaving is just an annoyance and not an emergency. You're right, your INR should be down within 24 hours, just from holding one dose. Having a physician who thinks that eating broccoli will raise your INR is more of a problem, in my mind, than anything else you have mentioned.
Hi, some antibiotics, medications and dark green leafy veg can all affect your INR. Vitamin K affects the way the Liver metabolizes and affects your clotting ability. Unless you eat the same diet every single day, then of course it will fluctuate. You could of course stick to the same daily diet for the rest of your life (highly unrecommended due to health). Just remember that you are not alone, millions of people world wide have fluctuating INR.