High Grade Lesion

I am a 43 year old female.  Recently had a stent implanted into my mid LAD the report says it was a high grade lesion.  LAD was 99% blocked.  I am curious as to what high grade means?  
The first time I had chest pains it came on while I was asleep.  It woke me up was fairly severe and lasted for 2 hours before just suddenly disappearing, Dr. tell me that I did not suffer a heart attack (thankfully) but I am curious about this first experience since it did come on at rest and lasted for 2 hours, would that be angina?   If so what type would it be?

[Darcy Green Conaway, MD]

High grade generally means lesions that are hemodynamically significant-- affecting blood flow. Generally, >/= 70%.
You probably had "unstable angina"