Four or five times per year, I get sudden and severe pain to my stomach, jaw/teeth, neck, and head. It usually starts when I stand up too fast and start seeing stars, which lasts for about 30 seconds. Once the stars go away, my abdomen, jaw/teeth, neck, and head all begin hurting very intensely, almost to the point of needing to go to an ER. This pain lasts between 10-20 minutes before gradually subsiding to the point where it disappears. Any ideas on what this might be?