The Others: a belated question [spoiler!]

(I did a search, believe me; if I somehow missed an existing thread on this movie, I apologize in advance)

I know I’m a little late with this, but I just saw The Others with Nicole Kidman and I have a question:

I understand everything about the end except why Nicole Kidman’s character had flipped out and killed her kids and herself in the first place. Did they ever explain that? Was it the migraines? Did she just inexplicably go apeshit?

I always assumed that

she was overwrought because of her husband’s disappearance and the stress of taking care of her photosensitive children.

However, I haven’t seen the film in a while, so I could easily be missing something.

This question (among others) was discussed in this thread (beware spoilers of course). There was one theory I suggested but I might’ve been seeing too much into the movie.

Thanks, both of you!