Walter Murch is perhaps best-known for his work on Apocalypse Now, where he did the sound design (for which he won and Oscar) and much of the editing. This is a passage from an interview about his craft and his career that he did with Emily Buder in 2015:
To be an editor, you have to be the kind of person who can be in a room for 16 hours at a time. You are working alone a lot of the time, but there are also times when you’re working with a director in the room. You have to be able to accommodate that. For feature-length pictures, it’s like running a marathon. You have to pace yourself over a year. When I’m considering a film, that’s in the back of my mind. You have to really like the project. Also, you are frequently away from home. You go where the director is. I was working in Argentina for a year, a number of years ago. Before that, I was in Romania, and before that I was in London, and then after that about 2 years ago I was in New York for a year. If you’re married, you have to find ways of coping with that and that’s a whole chapter unto itself.At the end of the film, it can be very disorienting when the work is suddenly finished. This is not exclusive to film editing; I’m sure it’s true of many other areas of human activity. Soldiers have this problem, actors who are acting in a play when the play is suddenly over, it’s like you’ve been cut loose: “Now what?!” This was never explained to me at film school. So when it first happened, I felt something was wrong with me. It’s the equivalent of a kind of seasickness; if you’ve never been on a ship before and somebody warns you about it, it’s okay. You’ll still feel just as sick, but you won’t feel like killing yourself. This is not that intense, but it is that kind of disorientation. And it passes, but it takes anywhere from two to six weeks to go away. During that time I would be very reluctant to try to decide what to do next. It’s like a love affair where you don’t want to bounce from one relationship to another; that’s dangerous. So, you should just let that project fade away and get back to normal, and then you can decide what to do next. We frequently don’t have the luxury of that, but that’s a goal.
That seems like a kind of mourning. When you work that long and with that intensity, you become attached to the film. When it's over, you've got to unattach yourself. That requires something very like mourning.