What can cause a high pulse rate and slightly low blood pressure? And what might they do for it?

One cause of an increased heart rate and decreased blood pressure is dehydration and dramatically increasing your daily water intake may change these numbers a little. But, I do not believe this is the primary cause of your problems. You have some sort of electrical conduction problem with your heart which allows the fast heart rate. There are medications which can slow this heart rate down but they need to know what this rhythm is (sinus tachycardia vs supraventricular tachycardia) in order to prescribe the correct medications. Your holter monitor should give then an idea of what is going on and then, hopefully, they will prescribe the correct medications for you. And, as your heart rate decreases, you should see a slight increase in your blood pressure. In the meantime, avoid smoking, caffeine and any prescription drugs (cough medications, etc) or street drugs which can contribute to this high heart rate.