I had a similar experience with my first stim cycle, but mine was a hormone-producing cyst, possibly even an egg follicle (I appear to have a demented reproductive system that can't ovulate on clomid but can on synarel). My clinic gave me a trigger shot to make it go away, which it did, and we were eventually able to continue the cycle after only a short delay.

You'll probably find that your clinic is used to getting phone calls from freaked out women (I know mine sure is!), so don't be afraid to call them and ask more questions. It's what we pay them the big money for!

BW