I'm SO glad to hear the good news, Donn! Congratulations! Just make sure you get the right dose, which is 2gr/kg/month, administered over a two-day period (usually, a 5-hour infusion process each day, which starts out very slow and then speeds up).
Headaches and allergic reactions are the most likely negative side effects, and that's why they should give you Tylenol and Benadryl ahead of time, and why you may want to take Tylenol for a few days after the infusion, especially the first times, until your body gets used to the IVIG.
Higher energy levels are a commonly reported and favorable side effect, especially for those of us who were debilitated by prior, frequent capillary leaks and all the attending consequences.