But amazingly the four-year-old boy - helped by his older brother - went to bed with his stump wrapped in a towel.
When his mother woke him up in the morning he said: "Sorry mum, I've gone and lost my arm. I didn't mean to."
An ambulance with a police escort raced the boy to a local hospital with the severed limb. But it was too late for surgeons to reattach it.
The boy is now recovering in hospital but is lucky to be alive.
Police spokesman Wolfgang Juergens said: "It is nothing short of a miracle that he didn't bleed to death in the night."
The accident happened when the boy and his 11-year-old brother played with an old washing machine in the kitchen at their home in the city of Ulm, southern Germany.
The appliance had been stripped down so the drum was exposed.
The pair switched it on and the boy's arm was caught between the revolving drum and the frame — before being ripped off.
But the older brother picked up the severed limb and put it in the family freezer.
Afraid to tell their mum what had happened, the boy astonishingly went to bed.
Police say an electrical defect meant that a sensor which should have not allowed the drum to spin while the front-loader's door was open was not working.