Renowned pediatrician Berry Brazelton explains that when a child has a new developmental spurt, they often lose some of their current abilities while they learn to incorporate the new skill or development. This is why when your little one learned, say, to walk, aspects of their speech might have regressed a bit during that time. It’s the same now that your child is older. You can probably think of “phases” they go through—often lasting one-to-four weeks—where they’re just not themselves. You repeatedly wonder, “Is she sick? Tired? Hungry? What’s going on with this kid?” And especially if this is your first child, you worry that this isn’t just a phase, and that they might be like this forever.
When this happens, there’s a good chance that some big changes are happening in their brain. This “spurt” of brain development could explain these “just not themselves” times. When I realize that this may be going on, it helps me feel more patient and nurturing when my kids act up. And I don't know if you've noticed this, but for my boys, it seems that they seem to eat more during these “spells” and sometimes experience growing pains overnight. Then in the next week or two I notice that they've outgrown their pants or shirts—in other words, their bodies are growing during these times as well.
The good news is that the phase doesn’t have to last forever. Eventually, your child will become themselves again, with another step taken toward growing up.