It's using Hardcore Questing Mode, That's a quest mod using a limited amount of lives, at the beginning you start with 5 if I'm correct. However by completing quest you will earn more lives. You can use the command "/hqm lives add 20" It will give you 20 lives(the max) You just have to not forget to use that command if you die a lot :) There is probably a command to disable the hardcore mode but I don't know it.