I've gone on about self editing before, but there's different types of self editing.
I don't think it's a good idea to go back and and edit your own work while you're writing. That will hold up the writing process and cause unnecessary problems if you're not careful.
The self editing that I think is ok, the type that I am doing right now, is when the book is finished and you're going back and fixing inconsistencies, spell check, and the like. It's exhausting and can be a lot on the brain.
It's been a bit more exhausting because I had an epiphany about the motivations and path of the villain that is introduced in Book 2 and I've had to do some reworking, adding and subtracting, and fine tuning.
But this is part of the fun, really shaping a book into becoming something substantial is part of the fun of being a writer.
I'd heard someone say that writing is rewriting and in some ways I have to agree.