I'm sure the ability to internalize the right pronoun is very dependent on context. If you've known a lot of trans people or are one, it's going to be easier. If you knew the person for a long time before transition, it'd be harder. If you rarely see them or have to think about it, it'd be harder. Probably! I'm sure people have different experiences.

I didn't try to get up out of bed, but I did ask the nurses a few times whether I was awake or dreaming. The anesthesiologist had told me I would have dreams, but I didn't! Unless the thing about talking to the nurses really was a dream.