For me, I stick to Dr Waldinger's definition of POIS, with is 5 criteria, the fifth being that symptoms disappears spontaneously after 3 to 7 days, usually.
For me it is clear that when there are persistent symptoms, there is something other than POIS that has to be diagnosed. This chronic something may be related in nature to POIS, and made worst by O, and could be fibromyalgia, ME/CFS, or similar, or depression, or something neurological. After a few weeks without O, if symptoms remain, that does not fit anymore with POIS definition, and this does not rule out that POIS will be present anyway after O, with its own symptoms and by worsening the symptoms of this other, chronic condition.
In my case, I have suffered from chronic anxiety. Yes, it gets many times worst when in POIS. But after a few days, it is just my plain, chronic anxiety that is left, not POIS.
Also, a step further, I remember having read posts on this forum from previous member Cornelius, I think, who said he never had POIS, he had an undiagnosed ADD or depression, or something like that, and when treated ( in 2011) for it, he had no more POIS symptoms ( as said in his 2013 post...not very active since).