A stolen dog with epilepsy was dumped in woods 85 miles (136km) from his home after he suffered a seizure, it is thought.
Anglo wolf-dog Ziggy, who requires daily medication for the condition, was taken from his home in Fulham, London, on Monday night.
He was seen wandering alone in Wrabness Woods, near Harwich, Essex, on Tuesday.
Tendring District Council said it believed Ziggy had been released after having an attack.
An inspection of Ziggy's microchip revealed he had been reported stolen and details of his illness.
Dog warden Adam McGoldrick said Ziggy could have died without medication he needs to prevent seizures.
"I have spoken to Ziggy's owner who is extremely relieved that he has been found safe and well, despite his ordeal," he said.
"Cases such as this show how important it is to get your pet microchipped, and then to keep the information on that microchip up to date."
Ziggy was re-united with his owner on Wednesday.