That is why the more productive and the less productive economies have a tendency to diverge. If this imbalance persists for too long, it will lead to problems like we saw during the 2011 European debt crisis, when several member states experienced major financial problems and all of us went through a deep recession.
Although it is hard to evaluate the absolute level of foreign exchange rates, relatively speaking, the yen is without doubt getting much stronger in the exchange market than before the Lehman shock.