Fast growing endometrioma?

St
Has anyone experienced one of these? Due to increased need to pee I saw my GP last week who arranged a scan. I have a huge cyst (10cm) pressing on my bladder.  My specialist called and said as its so big and has grown quickly it may be 'something nasty'. I had IVF on June and it was thought I had an endometrioma then but nowhere near as big. 
Now tomorrow I'm having blood tests and a CT scan to check it's not cancerous. 
Has anyone experienced something similar? I'm freaking out and hoping its just a huge, obnoxious endo thing and nothing more serious.