Diagnosis: My bite-off-more-than-I-can-chew <-> burn-out cycle was taken to be bipolar in my late teens. Burn-outs were seen purely as depressive periods, even when I felt none of the emotional effects of depression. My excessive cogitation and anxiety stimming were seen as mild mania, though I don't believe I have ever truly experienced manic episodes. Anxiety from social impairments was attributed to Generalised Anxiety Disorder as if my reported difficulties were figments of negative thinking. And my favourite - an Occupational Health assessment by a former employer where I was told that I had "Jesus Syndrome" (I presume they meant a "Messiah Complex", but even that isn't a recognised condition and in no way matches my traits - it's also very ironic as I have always been agnostic!)
Effect: Having a "known diagnosis" delayed access to subsequent psychological assessments for nearly three decades, hence no chance of actually getting to the bottom of the problem. Several spells of inappropriately handled CBT actually reinforced my self-esteem problems and prolonged burn-out periods. Standard treatments for bipolar were totally ineffective and were simply dropped without any alternative being explored. Upward spiralling anti-depressant dosages made life harder by sedating me to the point that I could no longer mask (at this point I assumed that masking was unconditionally necessary. I didn't even realise I was doing it most of the time; it was just "normal".)
Way Out: A very fortunate chain of events. At (yet another) referral for depression treatment, I saw a psychologist who knew autism well enough to see behind my mask and suggested the possibility to me. I mentioned this to the new CBT counsellor that I was assigned, who then arranged a case swap with a colleague who had worked previously with autistic people (autism wasn't part of her job formally, but she did understand it very well, and it restored my faith in CBT.) This counsellor then supported me to convince my GP to request a formal assessment, which was refused twice due to lack of funding to attend an expensive private clinic, which was the only one available at the time. On the third attempt, a new publicly funded assessment centre had been opened nearby, and I finally got to be assessed. The people who did my assessment were astonished that, given the extent of my autistic traits, I had never been flagged up over the previous 30 years - I was far from being the "borderline case" that I imagined I must be, just damned good at masking (and incredibly exhausted!)
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When you are fighting an invisible monster, first throw a bucket of paint over it.