Welcome to the forum....There are no Vets here & this could be any Number of things.....Do you have an Emergency Clinic in your area??? If possible, I'd head that way...Otherwise, he needs to see his Vet Tomorrow to diagnose the problem....
In tiny dogs, it could be a number of things....I would hesitate to guess, but you need to know what your dealing with in case of future attacks....
Please, come back & let us know what you find out.....