After reintegration, the combined innie and outie selves have a fear of elevators since they remember everything. If they can, they'll avoid it by taking the stairs or escalators. Irving was probably swearing but trying to keep cool and stay calm while his heart is pounding and his blood is running cold, momentarily convincing himself that he's going to face the horrors of the Severed floor again. But he grounds himself, talking himself out of it and willing his sweaty palms to go back to normal because he's free from Lumon. Even though he's not reintegrate in season two, it will be ten times worse once he is because he'll remember not just half a life, but all of it. He has all the memories now, but hopefully he'll have the macrodata team to talk this through with.
Helly has it even worse, because once she reuntergrates, she will have some Helena still in her, so it's a fear response either way. Both versions of the woman hated the situations they were in, but r!Helly holds r!Mark's hand as tight as he's squeezing hers, so they make it up that first terrifying elevator journey together with breathing excersises, and being there for eachother, even after the uncontrollable shaking and sobbing stops for them both.
(When I myself am faced with very uncomfortable situations, I lose control of my body and shake, even as I try to rationalise with myself. I believe that's my anxiety acting up. Recently, I've been sobbing so hard and so much I was having trouble gasping for breath. I also have an irrational fear of escalators, so I just try to focus on the knowledge of times before that nothing bad will happen)