When the psyche is hurting or in pain, why do we go into fetal position?

Regressi/nonspecific: This can have physical, and psychological impact on that patient. He/she may be in great pain on one side and so is in that position for comfort, or that many thoughts are going through his/her mind. This might be a form of regression if the patient is unable to deal with his/her problems. This is why support from family members, freinds, doctors, etc. Is essential to help with these issues.

Excellent question: We have stored within our brains (and therefore minds) all of our experience, newer ones generally more evident to conscious memory than very old ones. There is growing evidence that we "recall" in a sense, even pre-verbal experiences including going back pre-natally. These are not stored associated with language, but they are "evokable" via emotion. Pain perhaps evokes the protection of the womb.