I think we all have our own definition of stress.
My job times when I am VERY busy and others where I have literally nothing to do. To me the down times are the most stressful.
My boss is very demanding and impatient, he also tends to yell a lot. To others, this is very stressful and I don't blame them, but I've learn to manage him well so I don't stress over this.
Most of my tasks demand high concentration and everything is urgent so I am under a lot of pressure. However, I have to say I am nicely compensated precisely for this reason, so that definitely makes things easier