The term "spaz" has been used for a long time outside of the context of referring to cerebral palsy.
Many older people think that the work "sucks" refers to felati, but derogatory terms like "spaz" and "suck" have been modified by use so that the origin of the term is not referenced by the words in their new context. Eventually a word becomes so modified that one cannot tell what it means except by context. The famous four letter word is one such word, and its meaning can range from a powerful insult: "**** you and the horse you rode in on", to an invitation to romance: "let's **** like a couple of minks babe!"
Using the term "spaz-out" means to 'not remain calm' in the context that the writer used.