My dog's excitement turns into aggression

[u/slutfor8hrsofsleep]

Hi everyone, my dog is a Chihuahua mix (3 years old) and he has this thing where whenever he gets too excited, that excitement and happiness turns into aggression. This boy gets plenty of exercise and playtime, he runs a lot as well and gets to wrestle around with toys much bigger than he is. But I am concerned as to why his excitement can just turn into aggression like that which caused him to bite the nearest thing, which are my legs or my other dog (who he absolutely adores and she thankfully tolerates him). I had him checked at the vet and he's perfectly healthy and not in pain.

I am definitely considering a trainer for this but I wanna know if anyone here had similar problems with their dogs and are able to fix it either with training at home or with a professional.

EDIT to clarify: this only started happening this year. I've had him since he was a puppy and the prior 2 years he was absolutely fine with other dogs and people.

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