Basically, cramps occur because of overuse of a muscle, dehydration, muscle strain or simply holding a position for a prolonged period and sometimes because of probability of inadequate blood supply. But you mentioned that you have not over strained your abdominal muscles as you have not performed the agnisara beyond your capacity. Agnisara is basically abdominal pumping like vacuum pumping after exhalation. So, please ensure that you perform agnisara kriya in breathe out state and did it like pumping and that too only on empty stomach (after attending to natural call or 4 hours after your meal). You may continue for 10 seconds or even lesser only in the beginning and take deep breaths after each kriya.
If you continue to get pain after a couple of counts in Agnisara Kriya and stop it and check for probability of the other following causes and consult with your physician, if necessary:
- Indigestion
- Bloating (gas)
- Constipation
- Hernia
- Appendicitis
- GERD (Gastroesophageal reflux Disorder)
- Irritable Bowel syndrome
Sometimes, it may happen because of dehydration.
I hope that this helps and enlightens you on the subject satisfactorily.
Please share your case details to enable me to get into the depth of abdominal cramps after the agni sar kriya.