S.arah,
congratulations on the successful completion of your treatment.
It is not unusual to experience some odd pains right after the procedure, which may be attributed to the headframe positioning/pin sites. In my case, the left (non AN side) screw positioning was a bit problematic from the beginning, resulting in some tenderness and odd sensations that propagated throughout the cheek and jaw for about a month. The "good" thing was that it was the non-AN side, otherwise I would have freaked out thinking that something terrible was going on.
I also experienced infrequently the flash like pains you are talking about on the AN side - but they totally went away after about 6 months. I know that other forumites have mentioned these pains, occurring post radiation or surgery but I don't think anyone really knows what causes them. Ibuprofen generally took care of all these strange sensations.
Fullness is also common. BUT watch out for sudden hearing loss - make it a habit to check your AN ear on the phone regularly. In the case you notice sudden loss call your doctor right away and ask if he/she recommends steroids.
Take it easy, rest a lot and best wishes for a quick recovery.
Marianna