How to make the "sway" effect on weapons of FPS games

Question

I actually managed to make it sway left and right but I can't figure out how to do it vertically. Can someone please help me and explain what I have to add to the code?

extends Spatial

var mousemove
var swaythreshold = 5
var sway_lerp = 5

export var swayleft : Vector3
export var swayright : Vector3
export var sway_normal : Vector3

func _ready():
pass

func input(event):
if event is InputEventMouseMotion:
mousemove = -event.relative.x

func process(delta):
if mousemove != null:
if mousemove > swaythreshold:
rotation = rotation.linearinterpolate(swayleft, swaylerp * delta)
elif mousemove < -swaythreshold:
rotation = rotation.linearinterpolate(swayright, swaylerp * delta)
else:
rotation = rotation.linearinterpolate(swaynormal, sway_lerp * delta)

Answer 1

https://www.youtube.com/watch?v=a07CBMlxqWY

Hopefully this video explains what you are looking for (not mine).

Comments

This is gonna sound funny but actually I had no idea how to do the sway effect so I just watched Garbaj's second video on this topic, but it didn't explain how to do it vertically and I don't know how, so I'm just wondering what I can add to this.