First off, let me aplogize for the long post but I need to give you all the facts. About a month ago my 9 year old shih tzu woke us up in the middle of the night to go outside. This alarmed me because she never gets up in the middle of the night.....ever! Anyway she continued to wake us up every couple of hours. I knew she must have a bladder infection. We took her to the vets the next day and they did a urinalysis using an ultra sound. There were no signs of stones, but indeed she has a bladder infection. The vet put her on 125 mg of Clavamox twice a day. She did well for a few days until once again she woke us up in the middle of the night. I figured that perhaps the Clavamox was not doing the trick and took her back to the vets. They did an x-ray to make sure there were no stones stuck anywhere. They did another urinalysis and prescribed her with 25 mg of Zeniquin once a day. At this time I also had blood work done to rule out any bladder or kidney problems.
The test results all came back good. The vet said her bloodwork was great. I kept her on the Zeniquin for about another 10 days to make sure the infection was completly gone.
The problem is this: About once or twice a week she wakes up in the middle of the night. It is usually between 2:30 am and 3:00 am. She walks over to the door like she wants to go outside. At first I would take her outside and she would slowly sniff around and eventually go pee. Not in any big hurry, no realization that it was the middle of the night! 
After a few times of that happening she would jump off the bed, and I would go to her and say "come back to bed" and she would either turn around and follow me back to bed or I would pick her up and bring her to bed. She showed no signs that she had to go pee, but she was shaking as though we were getting a storm and she was scarred. She does not pant or show any signs of distress. I know she doesnt have to potty becuase in the morning when I take her out, she takes her good old time, sniffs and eventually pees. Last night she woke at 2:30, I went to see where she was and found her looking out our back door. I said come back to bed and picked her up. She came to bed, shaking slightly, curled up next to me and went back to sleep. It lasted less than a minute.
During the day she gets walked by her grandpa for at least an hour, but she also has piddle pads that she can use if need be. She does not use them. She is not peeing any more than she normally would when I am home.
She was always such a sound sleeper and never woke during the night until recently. Do you think something is distruping her sleep? I lay awake and listen, but dont hear a thing. Should I just let her be and let her sleep where she wants, not bringing her back to bed? I told her that shock therapy was going to be our next route! 
Anyone out there ever experience such a thing? Perhaps this is just Shih Tzu stubborness???? Any advice is greatly appreciated!!!