I don't normally have trouble with specific details, like which side of a character's face is scarred, but I have entire days where they're inconsistent in broad strokes. Stuff like height and shape face. It isn't that I've forgotten either. My brain knows exactly what they should look like. My hand is the one that can't figure it out.
But every now and then, those accidents look kinda cool and I'm like "Oh, okay, his hair just looks like that from now on." So it's good not to cling too hard to a design and get flustered when you can't make it work. You might surprise yourself.