I went to login to one of my Wordpress sites this morning and got a "server cannot be found" error. No Bluehost, no websites, nada.
Minutes later I got mySQL server connection errors but Bluehost was definitely back up.
After a few more minutes, all my mySQL based websites were back online.
Here was the Bluehost response. They didn't exactly say anything about the symptom that indicated that all servers were very briefly down but they did say the mySQL server had to be re-booted.