@Gargron take care of yourself in whatever way you can. Most of us do something useful every day. Even if it's just reply to an email, talk to a colleague about something or take the dog for a walk. You may never get to the bottom of the to-do list. But life isn't a to-do list it's just 'existing' at the end of the day. Seems like you've done a lot already. Hope you find a way to mitigate or reduce the stress and feel better about it soon. Also please ask for help if you can if needed.