My kid has a really strange habit. Every time she wakes up from a lunch nap, she seems sad. She would sit on the ground with her legs straight, her body bends forward, her arms are straight and crossed like an X and placed in front of her stomach, and head a little down. She seems sad but doesn't cry or anything. If I tell her to stop, she stops. But a few minutes later she would start again. If we leave her alone, she will just sit like this for one minute or sometimes more. One hour after she wakes up, she will forget about it and be happy as normal. It does not happen when she wakes up in the morning, only when she does after a lunch nap.
She has been developing this habit for around 6 months now. She is 24 months old now.
What is this, and how can I deal with it?