Loading Testing - Keeping Sites Alive
Have you done any tests on your site to see what happens under load? Frankly, you might be able to infer something from holding down F5, however basic that may be.
Chances are, if you've never even tried to place a load on your site, and you're using Apache with out-of-the-box settings, your site will fail the moment you receive a decent amount of traffic. Remember Commanment #9: if you're not an Apache expert, use Nginx.
I've previously written a guide to load testing over at TBB Polska's site. Have a read, and give it a try; it's possibly the most simple-minded guide out there, but it'll give you an idea.