抱歉是old self

根据句意，现在表现异常，明天就老实了，old self就是老样子的意思

朗文： be / feel / look like your old self ：to feel or look better again after you have been ill or very unhappy感觉/看上去恢复了原来的样子:
•It's good to see you looking more like your old self again.很高兴看到你几乎和以前一样了。