When CPI declines sharply, real GDP also tends to rise sharply.
I wonder if this isn't an artifact of NGDP as it is measured changing more gently than estimates of CPI. (I guess I should check the GDP deflator, rather than CPI)
Anyway, obligatory FRED graph.
Graph of 1-year % changes, real GDP and CPI-U from FRED ( https://fred.stlouisfed.org/ ). When CPI declines sharply, "real" GDP tends also to rise sharply.