For about five years now, I've been having what I call 'attacks' in which it feels as if I am being stabbed repeatedly. There is intense pain and pressure, I feel as if I am being stabbed in the side (near my gall bladder). (This has repeatedly lead doctors to believe that I have gall bladder problems. This theory has been repeatedly proven wrong) The pain is cyclical, in that it hurts for about a minute, and then I feel fine for another minute. As I progress into the attack, the pain last longer and intensifies. These attacks can last for entire days, completely incapacitating me, but I start feeling better after the attack culminates in vomiting. It takes anywhere from three to ten cycles (ending in vomiting) for the attack to cease. I've had tests for my pancreas, my liver, a hiatal hernia, and of course, my gall bladder. All of them have been cleared with a clean bill of health.
Other notes: This usually occurs once a month, but has little correlation with my period, and has happened up to three times a month.