A little PubMed time led me to this paper in the Journal of Affective Disorders " Association of seropositivity for influenza and coronaviruses with history of mood disorders and suicide attempts.", from whence the quote below comes.
"Seropositivity for influenza A (p=0.004), B (p<0.0001) and coronaviruses (p<0.0001) were associated with history of mood disorders but not with the specific diagnosis of unipolar or bipolar depression. Seropositivity for influenza B was significantly associated with a history of suicide attempt (p=0.001) and history of psychotic symptoms (p=0.005).'
So my personal observations have some basis in fact. My mind wandered to Encephalitis Lethargica, (EL) which if you recall, followed in the wake of the Spanish Flu outbreak at the end of World War One (the centennial of the commencement of which is this year). The cause of EL still is subject to debate; however, many studies have found antibodies to the basal ganglia in EL patients. This seems to point to an autoimmune origin, triggered by Spanish flu infection perhaps? That particular strain of the flu was noted to cause a severe cytokine storm reaction. Could this set people up for a later neurological autoimmune disease?
The most common estimate of the number of viruses in the world is 10^31. That is an astronomical number. With that many viruses, I often wonder how many fluctuations in our physical well being could have an infectious cause. How often do you wake up feeling a bit under the weather, but never bad enough to warrant a visit to the doctor. No one is going to go to the effort to hunt a virus for "the blahs".
Well, enough hypothesizing. I better get back to science that pays!