I have had this when I am on a high dosage of prednisone. It feels exactly like a heart attack! When I feel one coming on (they are pretty quick), I reach for a buscopan and my nitro spray. A few times, it has been so severe that the ambulance was called for me. They hook you up to oxygen, which helps a bit. This can be very painful and one time, my entire body went into shock from the pain and I was literally shaking from the neck down. Once my dosage of prednisone is lowered, the spasms usually resolve themselves. I hope this helps!