We had it too with DD1. It went on for a couple of months, then it was all over and she was back to her cheery self. Happened again after she turned three and again after she turned four. Each time, it gets a bit longer but she always comes back to being her normal happy self. The four year old one was the most difficult for me. I think because they can push it in different ways at that age. Each time it's happened, she's also had a developmental leap.

I know that probably doesn't help in the day to day of dealing with it, but you aren't alone