BPD involves intense outbursts of emotions that can happen abruptly, out of nowhere and go very high (and low) very quickly. 

What I'm wondering is whether the intense, deep emotions expressed are something everyone else without BPD expresses but our threshold (if that's the right word) is skewed or if there's a brain chemistry kind of thing that renders emotions to be more deeper and intensive than usual, or both. 

Hopefully I was able to articulate the question properly. Didn't know which flair was appropriate to the question.