Period barely lasted a day: endometriosis?

So, I have endometriosis, and normally I bleed heavily for about 9 days. 
I had mild cramping two days ago and my period only lasted a day. 
Then yesterday morning and this morning I suddenly got very pale, clammy and nauseated. I never did throw up and it passed after about 15 minutes. 
A friend suggested that the nausea was probably from low blood sugar in the morning. I'm just a little confused. 
My husband suggested pregnancy, but I'm not sold on that either. I know that a test would be the easy answer, but I was wondering if anyone else had experienced something similar?