Actually there was an article on HN a few days ago which differentiated work-related distress between stress (induced by too much work) and anxiety (induced by too little work).
It's become a nuisance in the background now after many years but each new task usually brings both these 'joys':
1) When I first get "Do/change/add X into the giant ball of mud of application that noone completely understands", I first get anxiety. Literally I have no idea not just how am I going to implement that but if it's at all possible. The definition of "anxiety caused by too little work" still goes, because I'm not "working" (not anything palpable like lines of code that can be measured and PRs be made). I'm just 'thinking', but that isn't much considered in business. Can't charge the customers for 'thinking', you need to produce.
2) Once I get familiar with the complexity involved and have some idea on how things can be solved, it's already too late in the sprint phase, it should have been done already. Now follows stress of delivering on time the 'commitment'. Not to mention that I usually implement half the task before stumbling into new evidence that changes the equation enough to require a different approach or further 'thinking' all while time is running out and commitments are not met.
Task solved, another one pops up, rinse and repeat #1-#2.