Stunned is an effect that gives a negative buff that is gained from being attacked by Zombies. It will decrease your Movement Speed by 90% the duration the buff. This buff lasts a total of 2 seconds and can not be cured, it must be waited out. Avoid this buff, by either killing zombies from range or dodging incoming attacks. You also have to watch out for getting stunned in the air, since it will count as falling for very long, resulting in death or broken legs.