Irregular cycles/ovarian cysts

I am currently on day 55 of my cycle. Experienced EXTREME pain bad enough to send me to the E.R. The Dr's advised me to see my GYN because it sounds like endometriosis. My sister had it at 22 and had to have a hysterectomy. I am so afraid to go to the GYN. I know I may not have it and if I do it may not be as bad as hers, but the thought alone is devastating!! Anyone have Endometriosis and willing to shed some light on what I may be in for?