Doing the gentle exercises they have given you helps to limit the swelling. Tingling is good, by the way - the medics would be worried if you didn't have it!
The SNB can cause all sorts of strange sensations in your arm: numbness, tingling, a feeling similar to bad sunburn, bruised feeling right down to the elbow. Mine had just started to subside after my SNB when they went in again to clear the rest of the lymph nodes. 4 weeks down the line and it's just starting to feel a bit more normal. I think it's something to do with nerve damage to the arm from where they go in. x