The action by the BOJ is not surprising. Japan's economy has had a weakened immunity system for nearly 2 decades now. This blast of cash right now might be vital in the BOJ's eyes, however one must remember that Japanese debt is already at 200% of GDP.
BOJ injects record cash to aid market
STABILIZATION MEASURES:Japan’s central bank also doubled the size of its asset-purchase plan to US$122 billion amid a plunge in equities and rise in credit risk