'Hidden'/forgotten past pandemics?

In the wake of Covid since the end of 2019, and now this Monkeypox thing and also the Hepatitis epidemic (mostly affecting children), plus not forgetting the almost annual media circus over Norovirus, I often wonder whether or not there were ever any 'hidden'/'unknown' pandemics in the past that we were unaware of and passed virtually unnoticed at the time?

I know I've already mentioned the following before in another thread, but one of the reasons why I'm wondering this is that back in December 2000 (at the age of 23 and 1/2) I had a really bad flu-type virus for well over 3 weeks that really knocked me for six, plus I lost my hearing in my left ear for approximately 5 days during said virus.

It was the worst 'physical' illness I ever recall suffering in my lifetime so far, plus my parents (especially my dad) were also ridden with it at the same time; a virus (and whose symptoms) would certainly send public alarm bells ringing today, but hardly anyone AFAIK made a big deal over it at the time, if it was fairly widespread. 'Phantom' Covid 2K perhaps?

What does anyone think?