Yesterday, i felt an enormous chest pain, and i couldn't breathe/swallow. my hands contorted and locked. my calf also locked, and my back arched. so scary & physical-can it really just be anxiety?

It is possible.: It would be important to have a com;ete physical to be sure there isn't an underlying medical condition. Best wishes.

Yes: Anxiety can be more disabling than other crisis thoughts because you loose control of your breathing and mental focus. Abnormal breathing can cause muscle and hand cramps or chest pain. On the first occasion, usually emergency care is chosen. Medications and lifestyle changes will need to be considered by you and your physician. Help is possible. Seek help soon.

Tetany due to hyperv: I suspect you had an episode of tetany due to a bout of extreme hyperventilation. This is most commonly seen in women who have extreme childhood abuse histories, but I have also seen it in some who don't have such a history. Tetany occurs when too much co2 is blown off when you are hyperventilating. This causes the muscles to contort, twist, and the back arches. It can be very frightening for the person experiencing it and for those who observe it.