Not because they need more logistics to keep everything going, as when you have four factions colliding at once and they all want different things.
But because they've emotional fraught. You're killing characters. Especially nice ones. You're throwing the hero out of his home and his home village and possibly his home country, and there's no way he's going to get back. Or he discovers that one of his companions -- or two, or three -- are plotting against him. Or after pages and pages, he finally gets to fight the Evil Overlord, or find the MacGuffin, or reach Cloud Cuckooland. Or . . . .
It gets ugly.
I've sometimes had to brace myself for it, but it's dangerous to work on something else because I might never come back and face it. And writing around the problem is worse. . . .
But one useful piece of advice is -- try to avoid writing them just before bedtime. Emotional agitation is not conducive to sleep.