Hang in there my friend. I don't suffer from clinical depression but this visa process sent me into a place I'd never been before - in the last month before my decision was made I all but stopped sleeping entirely, I cried ALL THE TIME, I was overeating and suffered from an ulcer. I was anxious every minute of the day and was obsessively checking over my application and refreshing my email. In the best of circumstances, this process is exhausting mentally and physically. Please take comfort from knowing that you are 100% not alone in your feelings and so so many people can empathize with you. I made a mistake on my visa application but caught it before I paid so I had to start over, which made me rethink everything after that. I would do exactly as the others have suggested and write a cover letter explaining the mistake, there are so many applications which have errors. If you want to try emailing Sheffield.SettlementDocsRequested@fco.gov.uk that is the email address that UKVI requests additional documents be sent to and I know several people who have proactively emailed documents there after they realized they were forgotten in their initial submittal. You will not receive a reply from that email address but they do definitely look at everything which comes in there. Just makes sure you have all of your application information on your cover letter and attach it to the email, and your email should also have all of your application information (name, application number, etc).
Please don't feel bad about seeking help for your metal and physical health, there is no shame in any of it whatsoever, and not least of all because we pay for it and you are entitled to care. And of course come here to all of us if you just need someone to hear you, this community cares!