My 5 year old shih tzu started to have aggresive behavior to us

Question
We have a shih-tzu since she was a puppy.  She was well trained by a professional trainer to be potty trained and listened to commands. She never liked to be brushed and would snap at me when I tried. But when I sent her to groomer she would be ok until two years ago, she bit the groomer once.  It got worse and not only will she bite, she will also bark with foam around her mouth.  This summer, her behavior has been very strange.  She is an indoor dog and has a bed next to us.  Lately she will try very hard to go into the backyard and hide in the bushes so you couldn't find her.  One time I looked for an hour and she didn't make a sound.  But when we take her back intothe house, she would be shivering and she would have this dazed look.  Today when I found her in the bushes, she snapped at me when I tried to get her.  Why is she not wanting to come in at night?  She's almost five years old now and she just started doing this.

Answer
Judy, I would have a vet check her out to make sure she isn't having seizures or something. If there is no health problems, I would suggest hiring a canine behaviorist to come out and observe her and see if they can offer any help. I'm sorry, but without seeing your dog in person, I cannot give you any advice.