The distraught mother turned to police after receiving ransom demands via message to her mobile phone.
She turned up at the police station in Parla, a dormitory town south of Madrid last Thursday despite warnings not to go to authorities.
She was told to leave €600 in cash at a secret location. "If you want to see your son again and live the rest of your life in peace".
Officers immediately leapt into action following established protocol for kidnappings but quickly located the 21-year-old walking freely around the town.
Under questioning he admitted that he had faked the ordeal because he was desperately short of cash and needed to pay an outstanding debt, a statement from Spain's National Police said.