If you look closely at all the icons in your System Tray (usually bottom right corner of the screen), there's usually one for the pointing device on a laptop. Right click on that and choose properties. Depending on brand and hardware, there should be an option on one of the tabs for disabling automatically when a usb pointing device (mouse) gets plugged in.
I lost an hours worth of email like this on my work laptop once - somehow multiple selected the whole damned thing, typed over it with a few characters, then couldn't get it back.
Vowed and declared I'd never do anything too complex without a mouse plugged in after that......
