You can skate straight across if you're not leaning in the slightest amount. That doesn't work on turns though.

If you can react fast enough, in 1/2 second as FB said since there is no warning, you want to twist your body opposite the fall so that you land on the back side of the shoulder and the muscle of your hip, slapping the ground with your inside arm and hand if possible. A slap, not thrust out under you. That's better than going straight down and landing on the shoulder (risks broken clavicle if it hits just wrong). It's hard to do in .5 seconds but not impossible.