Probably 5 or so. When I was sick off school I would binge movies all day long. Haven't done that in a long time though. I don't tend to consume film or series during the day so I don't really have time to watch so many anymore.
Nowadays it's usually 1 at most. But just as Dio said, when I was sick as a kid I'd watch a lot of them, as there wasn't anything else I had the energy to do. Many of those would sometimes be a bit shorter though and not actual movie length. Just VHS-tapes with things like "Really Wild Animals" for example. I still count those as movies, just shorter ones
I've watched The Lord of the Rings trilogy in one setting on two separate occasions, which probably counts for five or six films if not more.
I also watched Avengers: Infinity War before seeing Avengers: Endgame in theatres which is around 5 1/2 hours of movie, though that pales in comparison to the time I watched Half Blood Prince and Deathly Hallows Pt. 1 the same day I saw Deathly Hallows Pt. 2 in theatres and in fact I watched the previous 5 movies over the course of two days before that as well.
I think I also once watched the original Pirates of the Caribbean trilogy in one sitting.