In Every Day, what does A do on the days s/he doesn’t want to be someone else?

When A takes on the identity of Justin, s/he isn't very happy about it. Justin listens to loud, obnoxious music on a loud, obnoxious radio station with loud, obnoxious DJs. The rest of what A needs to know about him can be accessed from Justin's memory: the way to school; which parking spot he uses; the combination of his locker; etc. But even with all the relevant info, it's still hard for A to go through the motions of adapting him or herself to a new identity.
Whenever things get too tough and A can't imagine maneuvering him or herself through a long, hard day at school, it's time for A to stay at home. S/he'll phone in sick and stay in bed reading books. After a while, this gets tiresome, and A eventually finds that s/he's up for the challenge of a new school and new friends. But this feeling only lasts for a single day.