My girls love being brushed and I always get tons of loose fur off of them. The first day I am back from work I get LOADS off of them, especially Boo. Until she would allow me to brush her, her fur would fall off in big clumps all over the place and I always get more off of her everytime I brush her. I pick up the grooming tool and they line up and beg for their turn. Amy would let me brush her until she was hairless... she REALLY loves it.

It is summer so I am sure your vet was right about it is happening in many pets.