Yes, after Bear replied it occurred to me that I haven't done a deathmarch on a heavily mental activity like novel writing. If I do, it's self imposed and I can stop before I kill my brain.
(School essays weren't self-imposed, I grant you, but they also weren't as long or involving pulling out the heart.)
My comparable deathmarches have all been on activities of crafty kind, like ceramics. Which leave the mind more open to roam.