Our thoughts, change our feelings and the feelings create the emotions. Emotions are like control system to our body. Your blood pressure is all about what you are thinking consciously and sub consciously. Rather more with sub conscious thinking.
Therfore you might want to observe your thoughts, see if there is anything that you are stressing about.
Next Steps
Observe when is your blood pressure going high and when it is going low. So that you get the pattern.