You lose 30 exp points and must either have Reraise up or have someone else raise you to get the exp points for that campaign battle
-You don't lose any exp for dying, i believe the previous answer is referring to the exp you gain from the battle itself, you lose 30exp from the total each time you die. Also should the battle end while you are dead, you can still raise afterwords to gain the exp/allied notes.
- another thing to note is in order for all this above text to work, you must have the allied Tags effect on. If you forget and walk into the battle without tags and start attacking the first thing you see... you can gain skill ups however you will lose the appropriate amount of exp if you should be KO'd.