**** Not a teacher ****
'However it is labelled' means 'however it is described or classified or categorized'. 'Post-traumatic stress disorder' is one such label or classification or categorization.
Sorry to say, but the part in the brackets does not sound correct ("will sometimes do" - does not make sense) - but I am guessing that it means that PTSD is sometimes labelled differently. I think the part in the brackets should be "as it is sometimes done with PTSD" ('as it is sometimes done' = however PTSD is labelled/categorized/classified).
Student or Learner