hydrochlorothiazide will cause you to lose potassium so essentially your levels should not drop.
25 mg is the normal dose for
hctz. There are stronger diuretics out there so these are not "too high."
If you are worried about lowering your BP, just watch for signs of dizziness, especially with prolonged standing or when you change from a sitting/lying position quickly up to a standing one. If you feel faint, you may want to discontinue the medication.