About the only thing you can do at this point is contact your web host. It could be a corrupted database, but it sounds more like a connectivity issue.
I'm having the exact same error, getting batches of 10 or 11 of these emails message at a time, and having contacted my web host, they have checked their servers and report no issues.
I don't have any reason to doubt them, as the support from my web host is usually first class.
I have other apps using the same MySQL database server and they all work fine, yet OS Ticket has recently started doing this and performing very slowly.
For info, my database is only 0.17Mb at the moment, and the database passes all integrity checks.