As long as you don't do any actions...well besides moving...you are 100% immune to all damage save for like enrage type damage for like...10-15 seconds.
People who get up only to be put down generally got up and immediately started attacking. It's best to be picked up and wait for a healer to top you off a bit before you resume the assault...or more than likely you'll eat dirt again on the very next raidwide.
