That was the 90s.
Because of all the costs of reunification.
That's a long time ago.
Though it doesn't really seem that way.
It’s not all that long ago. And citing the “costs of unification” alone is an oversimplification.
The major event shifting things in Germany’s favor was the creation of the euro. That currency, even born as a fiat currency, was designed with the German bloc in mind, and was detrimental to Club Med and the British sphere. The euro’s central bank played some very nasty interest rate games between 2007 and 2008 as well.
OK. That had crossed my mind, but I think to call it the "sick man of Europe" was inaccurate. The reasons for Germany's fiscal problems at the time were clear to see. Its economic output, however, remained strong and growing.
When the UK was termed "the sick man of Europe" in the early seventies, it was quite accurate. The country was stagnating under its socialist welfare structure.