I think that if you are asking this question, then you probably already know that you need to cut back. I just recently started working part time (my first job ever). I am working 25 hours a week and I already plan on asking to cut back to 20. 5 hours a week doesn't seem like a big deal, but it's that last hour every day that really seems to wipe me out. Just remember that your health is not worth sacrificing for that extra money that you earn by working more.