First day on keto and High Blood Pressure

Hi everyone! I have a serious issue: I've been in and out of keto diet for quite some time, and sometimes I make a carb loading day(usually on Sunday) and on the next day I start keto again. And every time on this day I get a headache, but the last time I had a headache and very high blood pressure also (160/110). But the next day everything is back to normal. What is it?