This is cute and all, but why is Sophie going to bed in the middle of the night? Was Akari up until like 6AM (in which case she's going to be a zombie at school no matter what)? Did Sophie decide to take a nap randomly?
My interpretation is this:
1. Sophie watched something scary
2. She's worried that she'll have a nightmare if she sleeps by herself
3. She decides to sleep next to Akari so she feels safe
4. She might have gone to bed earlier than usual because of Akari saying that Sophie will fall asleep before she does
Alternatively: Sophie has a weird sleeping schedule