See an opthamalogist as soon as possible!
It could be vitreous detachment or retinal detachment or ?? - only an opthamologist can tell you.
My own retinal detachments (one 3 months ago, another last week) appeared to me as shimmering dark, circular, temporary areas that appeared when I moved my eye, then disapperared momentarily, that were in the same area over time, that grew larger and more persistent with time. There were at times flashes of lights, that I could especially see in the dark. I've had lifelong floaters, so the definite increase in number and in darkness of floaters I saw was confusing - was it the same as before or different? The "curtain" that is described only came after several days of the "shimmering" and flashes. I can see how your description might be describing the same thing.
In my first detachment, I wish I can sought more prompt examination, as I waited 3-4 days after noticeable symptoms. Websites gave me information, but I shouldn't have dallied around. With the second one, I recognized it within a day, and got seen the next day. Both time, at first I didn't want to believe its real and happening to me, but sure enough it was. And I learned that time is of the essence - the longer the detachment, the more chance of permanent damage. Don't mess around with your vision!
You situation needs a medical eye exam from an ophthalmologist as a starting point. Find one near you at www.aao.org
JCH MD