With the slide through you could just play a character animation montage, which would be progressed by the w key (you could layer on some sort of idle breathing when the player is not progressing the animation).
If the player “loses control” on the stairs and the character just runs up / down them them and then regains control at the end, then I have that in the scene I sent. (hard to tell without playing it)
Not sure why you would not just have normal motion on the stairs though?