I don't know if it is connected, but 6th century is when the plague of Justinian happened and it spread to Northern Europe too. In 536 there was a volcanic winter, one of the worst climate-impacting events in documented history that started an ice age. Was a pretty tough time to survive in general.

"Original" depends on what time period you're referring to, because the people before the Slavs weren't there for that long themselves.

https://en.m.wikipedia.org/wiki/Indo-European_migrations

But in reference to the Slavic migrations, I think they likely headed west and south:

https://en.m.wikipedia.org/wiki/Migration_Period

It was so shit an boring they simply turned around and left.

spoken like a true Polak!