Help! Really fast heartbeats & trouble breathing when very scared, worried, & stressed?

I'm 17 years old and I've been experiencing moments where my heart beat will rapidly increase & I'll have trouble breathing (causing me to cough & take short, abrupt breaths to breathe). And my body will get extremely weak.This seems to only happen in times where I'm extremely stressed & worried. For example, it happens when my girlfriend talks about breaking up with me (sorry, it's the only example I could think of). Because I love her, it makes me very scared and anxious. So when she talks to me about issues revolving around breaking up I get the symptoms I described above.

I also have very high cholesterol levels (if that helps).