I have had two periods of great work stress times in my life - the first was when my startup was under enormous financial strain and I was doing everything I could to hustle up the money to keep the team together (2002 to 2003). This was a time of lying awake night after night wondering what to do.
The second time was different. I was working two more than full time jobs (academic and running startup that was taking off). I literally did nothing for a couple of years (2010 - 2012) but work, eat and sleep. At the time I didn't feel stressed (I was comparing how I felt with the early stress times), but I was under a lot of stress. I only realised when I quit my academic job.