Puppies capture hearts with their endless curiosity and boundless energy. But in little Mila's case, her excitement is a big problem.

Erika and Ryan Lil had been worried about Mila since the day they rescued her. Whenever she would get worked up, she'd fall fast asleep.

"I didn't know what it was," Erika told Inside Edition. 

"Her whole body just loses function, her feet give out from under her, she'll pass out," she added.

The couple took the pup to the vet, who diagnosed her with a rare neurological condition called cataplexy narcolepsy, triggered by extreme excitement.

"She doesn't know what's happening. It's very quick. It's not painful for her unless she hits concrete or driveway," Erika said.

And what's the most exciting part of Mila's day? Eating.

The couple recorded a video of Mila chowing down, and she falls asleep mid-chew.

"I think we're happy we rescued her. Many people would give her up with a serious condition," Erika said.

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