Hi Hon,
I know, it's very stressful. This happened to me five years ago, when I was 40 years old. My period (which was always erratic my entire life, with very long stretches in between my periods, and when I did get a period, they lasted for 8 days) suddenly became very, very close together (like 21 days, then 19 days, then 18 days, when my periods were usually 31 days apart and sometimes even 61 days apart) and I had very, very heavy periods with lots of blood clotting.
It scared me to death! It was SO not normal. (although my periods themselves weren't normal either)
I too underwent an ultrasound, and the GYN found hyperplasia; mine was 11 cm. Probably caused by my very erratic periods in which my lining never sloughed off enough and so it just kept building up over time.
I opted to undergo a NovaSure Ablation (NA), where they burn the inner lining of the uterus off. In my case, it stopped my periods (yeah!) as well as it makes me unable to have children (which is okay, as we have one daughter and we were done having kids; I had already had had my tubes tied before having the NA done). My GYN did a biopsy before she did the NA surgery, and the biopsy came back negative for cancer. What a relief. I was not asleep when she did the biopsy--it was done before I went to the hospital to have the NA done (I think it's done almost like a Pap smear, if I remember correctly).
Try not to stress out until you know all the facts; then you can make a decision as to what to do. I know; easier said than done. For me, the hardest part was having everything done fast and quick, because I was concerned about whether or not I had cancer. And I was immensely relieved to discover I didn't. After that, it was a piece of cake to have the Novasure done. I didn't want to give my body any help in deciding later it should develop cancer; I nipped it in the bud.
Oh, and I did not have Endometriosis. My mom and sister have it; my OB/GYN actually did an entire check of my female organs while she was in there doing the Novasure (I have pictures). All of my female organs were fine and healthy with absolutely no sign of Endometriosis. Although that probably can be the case for some, it wasn't for me.