Many now complain of "earthquake sickness" -- the sensation that the ground is swaying beneath their feet even when it is not -- a condition blamed on confused inner-ear balance receptors and a heightened state of anxiety.
For the tens of thousands living in spartan and crowded evacuation shelters in and near the tsunami wastelands, the creaking of already weakened buildings and the risk of another killer wave spark mortal fears.
"We are almost getting used to the aftershocks, yet every time one of them strikes, we are reminded of the terror we felt the day of the tsunami," said Kenichi Endo, 45, who lost his fisherman father at sea to the monster wave.
"I become afraid that maybe it will return," said Endo, now one of 790 people holed up in an elementary school turned evacuation centre in the devastated port of Onagawa in Miyagi prefecture. "I have flashbacks."
In Tokyo too, where buildings have been shaken and trains halted by quakes, millions are put on edge every time a shrill seismic early-alert tone sounds on TV or their mobile phones, warning of a fresh threat.
Hundreds of aftershocks worsen Japan's quake trauma | ABS-CBN News | Latest Philippine Headlines, Breaking News, Video, Analysis, Features