Last Sunday, I had a sensor go bad a few days early. It just started giving wacky readings. Just about the time I did a full download of it on a new computer.
Smart thinking -- I downloaded the data the next morning. Called Dexcom tech support when I had time to talk, and was able to remotely access my Dexcom program (through gotomypc), and sent Tech Support data. Worked with them for two days via email, but the sensor never did straighten out.
I swapped sensors a day early and the new sensor has been night and day different. In fact, I am on day 8 now.
The best news, they sent me a new sensor.