For is used as an introduction of reason. I consider, the reason of what happened in the first clause should be introduce with For (used as coordinating conjunction) in the second clause.
"She must have been tired, for she fell asleep the moment she inclined her head." (Nikos Kazantzakis, Report to Greco, 1965)
The above sentence is doing opposite to main idea.
I think it should be written as
she fell asleep the moment she inclined her head, for She must have been tired. Please elaborate.