I take medicine for high blood pressure. If I dont take it for even one day, my blood pressure goes up significantly. Should I take this medicine on Tisha bav and Yom kippur?

Speak to your doctor to establish the danger of your high blood pressure. If you risk your life by not taking your medication, you must take it, if you can easily skip a day without any medical implications, you shouldn’t; for any intermediate case you should consult your rabbi. One should also remember that medicine is not food and if taken when needed it does not mean you have broken your fast – therefore Halacha will be quite lenient with this issue.