My three way lamp is suddenly just one way. Is this an electrical problem or fire hazard?
The most likely explanation is that one of the two filaments inside 3 way bulb burnt out or broke. 

If it was already close to burning out before you moved the lamp, the mechanical shock of moving may have broken it the rest of the way -- perhaps it broke completely so you didn't see the characteristic "flash" of a filament burning out when you turned on the lamp for the first time after moving it.

You could test the lamp contacts in the socket with a continuity tester at each switch position to verify that this is the case, but a much easier (and definitive) test would be to replace the bulb with a new 3-way bulb and see if it works.