Pacino was probably stoned, and Coppolla told him to take a shower and a steam bath, and get sober for the next shoot.
I love him as an actor but he's always been a prima dona and now that he's getting ready to find out if there's really is a God and if Pacino's really the devil, he's starting to get scared.
No movie is ever shot “in order”.
‘I think the old drunk is hallucinating, the shooting scene in the restaurant {if shot in order} was after the wedding, the shooting of Vito, the hospital scenes, the fish in the vest, the “going to the mats”, in other words, too far into the movie to replace Michael.’
If there is one thing we know for sure is that The Godfather was NOT shot in sequence. When you have actors that appear for two minutes every half hour in the movie, they do not shuttle them (and the sets they appear in) in and out of the studio.