Chris,
I can only tell you that I felt my DAVF was changing quite rapidly: My Update - Dural AVF Embolization
You need to judge what’s going on and tell the neurosurgery team or your primary doctor (as an advocate for you, perhaps) what’s going on. You’ll see in the linked conversation above that I worried in much the same way as it sounds you are worrying and I’m not sure I held back in telling the neurosurgery nurses about how I was or telling my GP how I was. My approach was to give them the information to judge whether I was ok to wait until the beginning of April for my op or whether it sounded more urgent. In the UK, treatment is free – paid for through taxation – but what that means is that there is limited capacity. I didn’t want to elbow my way to the front of the queue at someone else’s risk. I just wanted to ensure the information was there to make the right decisions (and you’ll see me being concerned that it might prove too late 
)
I’d say it was my GP who relayed what she could hear of my DAVF (and the area on the back of my head where she could hear a bruit) that finally drove a decision to get me in.
It’s a worrying time, I’m with you.
Stay in touch 
Richard