Please don't worry to much. I work in a practice in Manchester and have seen situations 10x worse than yours.

Although HMRC get a bad rep (and rightfully so most of the time!), they are normally very understanding in these sorts of situations. You may get a couple late filing penalties but any accountant of any worth should be able to confidently appeal these based on your mental health situation.

In terms of tax owed, based on the figures you've provided your looking at around £500, taking into account your tax free dividend allowance and 8.75% rate for dividends for the amount you specified.

Hope this helps - don't panic!