By the time Joseph Smith and Sidney Rigdon received the vision of D&C 76, Joseph had already seen and experienced multiple visions and experiences (and in many of these cases he reported being exhausted).
Philo Dibble recorded the following:
Joseph sat firmly and calmly all the time in the midst of a magnificent glory, but Sidney sat limp and pale, apparently as limber as a rag, observing which, Joseph remarked, smilingly, ‘Sidney is not used to it as I am.’– Elder Philo Dibble, “Recollections of the Prophet Joseph Smith,” Juvenile Instructor 27, no. 10 (1892): 304
Why was Sidney limp and pale but Joseph sat firmly? Why would Philo Dibble say this if the vision was fake?