"Pure OCD"

[Angrboda]

ETA: I just learned that this is a neuropsychological condition, rather than just a mental illness. Nonetheless, I think the anxiety it creates is enough to warrant calling it a mental illness. It is my understanding that the "neuro" part is what makes the thoughts repeat and become intrusive. The mental part is where it freaks you the fuck out.

I am not a doctor, but it's my understanding of what I have been taught that all or most Axis I disorders are believed to have an organic, biological, or neurological basis. This is opposed to Axis II disorders which are typified by the personality disorders, which are presumed learned behaviors. (Note, this is not an absolute distinction, as persons with borderline personality disorder can experience psychotic symptoms more typical of Axis I, and while the affective disorders such as depression and manic-depression are Axis I [IIRC], it's not uncommon to see serious depressive episodes [if one wants to call them that] which are caused by situational factors such as the death of a loved one, or stress, or sleep deprivation, but in an otherwise normal subject.)

And unfortunately I lost my breadcrumb, but there was a phrase in something I passed over which described OCPD as OCD without the obsessive behavior component. I'm not well read on either OCD or OCPD, but that sounds a lot like what you are referring to as "Pure OCD" (though OCPD often presents with symptoms in addition to those you describe). Anyway, worth looking into, perhaps.