Are you by any chance using an iPad? The iPad2 has been tested (and was positive) for causing shunt valves to change adjustment due to the magnets inside the tablet. I have to keep reminding myself while I lug around my iPad in my purse to keep in away from the shunt - wear my purse off the other shoulder. I have a newer iPad, but I don't want to take any chances.
Not sure if carrying a laptop would do the same. It is not just the carrying either. It's using the computer on your lap too close to the valve.
Might this be a possibility?