Complex sentence: A prominent and often disturbing symptom is that in the experiences of altered body image: the person may find that he or she is confused as to the size and shape of parts of (or all of) his/her body.
Split into simpler sentences: A prominent and often disturbing symptom is an experiences of altered body image. The person may find that he or she is confused as to the size and shape of parts of (or all of) his or her body.