I have a mare that did this. We thought she was colicing but you could hear gut sounds plain as day, and she would also do this during her heat cycles. Others and including my vet thought it was a possibly cyst on her ovaries. The vet recommended taking her ovaries out. I didn't do that but instead I am giving her the SmartMare Harmony supplement by SmartPak. It took a couple of months but defiantly saw significant improvement. Very rarely have I seen her do one of these what I call "episodes" but no where near extreme like they were in the past year. Now taking her ovaries out is still not out for me, due to I have decided not to breed her due to this and also she had colic surgery late last year, I am just afraid she could not handle the pregnancy.
But this is something I would consider giving her. Also have the vet do blood work to check your mare's hormone level. It could possibly help to determine if she has a tumor. My mare was right in between mod to high so wasn't much help for me lol. I haven't retaken the blood work yet ever since I've used the supplement but its suppose to help the mare's hormone level.