Spontaneous recovery means the reappearance of a previous extinguished response. For instance, Jon is scared of dogs because he thinks they look angry. After a long treatment, he finally gets used to play with the dogs. He is no longer afraid of dogs. However, one day he saw a dog walking towards him, he suddenly started to fear again. His fear was extinguished after the treatment, but he suddenly recovered that response again. This is more of an one time event.
