80/60 while lower than normal is fine provided its generally your normal blood pressure and, you don't have any other symptoms associated with it. A good test is to lay down then sit up quickly. If you have any dizziness
or light headedness, then there it is probably too low. 76/47 is definitely too low. If you have that again, I'd definitely see a doctor. Also, some medications can have side effects of lowering blood pressure. If you are taking any meds, mention this to your doctor on your next visit. My BP is normally 105/70 but I was on some meds for stress
a while ago and my BP was regularly 80/56 while resting yet I had no noticable effects from it.