I have an intense phobia of dentists; if I were wearing a constant monitor, I bet you could tell when I was at the dentist just by watching the blood pressure and heart rate spikes. (You'd have to find some way of differentiating them from me being in a car accident, or being attacked by a werewolf.)
I wonder if it would show up on the heart rate (or heart rate variability) tracking from an Apple Watch or similar. My Garmin picks up stressful events all the time.