Learning about Bandwidth

One of my sites ran out of bandwidth last week. It was only for a few hours before I noticed it, but since it happened, my traffic has taken a serious dive. This is so frustrating, since I've been working really hard on this site to get it more traffic. Previously, hostgator would send me an email at hitting the 80% mark....but no emails this time until it was too late. Grrrrrrrrr