I had my SIS last week. It went very well. I have a sensitive cervix, and whenever anything touches it (paps included) i have bleeding afterward. For me, the SIS was uncomfortable and painful enough that I needed to take deep breaths to get through the part with the saline infusion. I think every woman is different, but deep breaths (slow in, slow out) really helped me. It also goes really quickly! It only takes maybe a maximum of 10 minutes. The vaginal ultrasound occurs simultaneously and it all goes really quickly. Following, you'll be a little bit "leaky" so you'll want to wear a pad. I had minimal cramping following it, just like period cramps, but they were gone by the evening. MY RE told me to take 600mg of advil/ibuprofen beforehand. I'm glad that I did...and then I came home and enjoyed a glass of wine. :)
I'm sure it will go well for you - just think "crampy at worst, maybe not much of any feeling at best!" That oughta get you through it. :) GL!