As mentioned elsewhere, the stress comes from outside influence in my view, but by outside I mean away from the console i.e. management re-organisations, efficiency campaigns, poor level of support. But the actual job itself is quite relaxing because it works with efficiency compared to those outside influences....probably being in control liek someone said.
In my view probably most stressful is dealing with different personalities...just like there are certain captains that when you fly with them you probably dont relax as much as with others.