At 100/64 you are on the lower boundary of normal blood pressure, but I don’t think you would qualify for what is considered “low blood pressure”, especially since you sound like someone who is athletic and exercises regularly. I believe they consider low blood pressure to be having a systolic pressure number of less than 90 or a diastolic pressure number less than 60, so neither of your numbers (from that one reading) would officially qualify you for low blood pressure.
Low blood pressure can absolutely cause dizziness, but I don’t know that it has been linked to the constant disequilibrium you are reporting. I think it is more linked to the lightheaded/feeling faint/sudden unsteadiness kind of imbalance than any kind of chronic imbalance, but I am absolutely no expert. I’ve had a moderately high systolic pressure number combined with a very low diastolic number for most of my life, though my systolic number dropped greatly once I left a job that was slowly killing me about 6 years ago. I found that the nortriptyline has greatly raised my diastolic pressure, as it has raised my stading heartbeat probably 10-20 BPM on average. I’m glad to be off of it–I want to see what my heartbeat and pressure readings return to now that I am. I have loved having a naturally low heart rate and diastolic pressure my whole life and I didn’t like the fact that nortriptyline seemed to counteract that in me.