Error establishing a database connection

So, my WordPress site has, it seems, randomly stopped working. All I get when trying to access it is “Error establishing a database connection”, and I can’t access the WP admin dashboard either.

It’s been working fine until now, except the backup plugin I had installed seemed to have stopped working, and now this… (Well that, and the site has been working kinda slow lately.) I don’t get it, I haven’t made any alterations to the site lately, all of this just seemed to randomly happen on its own.

Any ideas? Should I freak out or is there anything I can do?

EDIT: Okay, site seems to work again. The backup plugin still doesn’t work because “wp-cron.php is returning a Operation timed out after 30006 milliseconds with 0 bytes received response which could mean cron jobs aren’t getting fired properly.” which I suppose is still not exactly ideal.