I've heard of this happening. Since Watchtower teaches that attending all meetings and assemblies is essentially a prerequisite for everlasting life (as is monthly "field service"), the meeting becomes more important than life itself when the reality is they are a waste of living.
Not as dramatic, I've seen an older CO feel faint in the middle of a Thursday night talk and have the PO take over for him from the outline. I've seen another older CO feel faint, almost fall, but he decided to give the rest of his talk sitting.