I once had sever eye twitching, like you describe where I could feel it but no one else could see it.
I had it checked out by my GP who said it was related to stress and using computers
too much at work and at home.
It lasted a while but now it only happens when I get really stressy.
It could be something like that, don't worry too much about it - have the scan and see what the results are.
I'll keep my fingers crossed for you, hope it all goes well.
Keep us updated!!!