Board Thread:Naruto Discussions/@comment-26636534-20180325094649/@comment-34752936-20180325134115

^It is stated in this wiki that if a victim is forced to experience a drastic passage of time in the fraction of a second Tsukuyomi is actually active, the stress on their mind would kill them, even if the genjutsu was a happy and peaceful one, such as when Itachi uses this technique to kill Izumi Uchiha by having her experience decades worth of time in a fraction of a second.