Several Database Issues after Repair

After receiving the dreaded “Error Establishing Database Connection”, I followed the guide here, http://www.wpbeginner.com/wp-tutorials/how-to-fix-the-error-establishing-a-database-connection-in-wordpress/, specifically this bit, “define(‘WP_ALLOW_REPAIR’, true);” then going to, http://www.yoursite.com/wp-admin/maint/repair.php and selecting “Repair”. After doing this, I was told to paste the below in these forums;

wp_comments: 19 clients are using or haven’t closed the table properly
wp_options: Table is marked as crashed
wp_postmeta: 3 clients are using or haven’t closed the table properly
wp_commentmeta: 19 clients are using or haven’t closed the table properly

No idea what this means or how to resolve this problem or what caused the problem in the first place. Strangely, the “Error Establishing Database Connection” error occurred without me doing anything. This is on a website that gets a reasonable amount of traffic per month but has been left still for quite some time, other than basic plugin updates etc. (last time any updates were made was around 2 weeks ago, and all was find until today, which suggests that it was nothing related to this which caused the problem).

Michael