I just experienced a high amount of stress from a brief event and noticed that whenever I checked my heart rate when I'm stressed it's usually much lower (like in the 60s), when my resting resting heart rate is averaged about 90-100. 
Everything I looked up is just about living with anxiety, not having just small moments of it, like being jump scared, or giving a presentation or working in customer service. All videos I see of people being scared there heartrate goes up, not down