When I logged in to cPanel, I found two php files that looked like http://pastebin.com/Hwqi2ynK. I moved them out of public_html and changed my password. Then when I tried to log back in, I got "This account is currently locked out because a brute force attempt was detected." I can't say for sure that this was the cause, but I have no idea what else could have caused the high server load. In any case, it was probably a good thing that my account was suspended, or I may never have noticed.