I don't monitor my BP, but when i went to the doctor they used one of those wrists BP cuffs and it said something outrageous like 150/105 and my BP has never been that high. They took it again and it was lower, the nurse said it could have been because I was moving.
Auto BP cuffs are not as reliable as a manual one. If you get an abnormal reading I would try taking it in both arms and go from there. You will most often get a different reading in both arms.
How far of a break did you take between times taking it? Just seeing that result (178/156) would have made my BP go up! I think if your BP were that high (and it is not normal for you) you would be symptomatic with a definite headache.