1) You're in luck, there is a lot of evidence to show that this kind of thinking responds very well to Cognitive Behavioural Therapy. There are a number of ways to get this; you can do it from a book ("Mind Over Mood" is one recommended book) you can do it online (the Australian "MoodGym" is often recommended) or you can buy therapy. Look for someone experienced and registered. In the UK you can go to your GP and mention IAPT (Improved Access to Psychological Therapies) but keep pushing it, some GPs say there isn't any when there is - you may have to ask your local MH trust about talking therapies.

2) Remember that tech invites high performers, and HN has a bunch of VERY SMART people. Don't compare yourself to them; you'll always feel lousy. Compare yourself to the people behind you on the bell curve. You are above average, and for the moment, that's good enough. Now you just need enough motivation to plug away at the good ideas, and keep producing them until you get the awesome ideas.

3) Make sure your food and exercise are good - there's lots of evidence to show that good exercise helps with mood. And eventually it may lead to team sports, which have a bunch of social life benefits. Alcohol will lower mood. Some people find that even small amounts of alcohol will lower mood for days. Being careful with sugar, caffeine and alcohol should help.

4) Learn a time management technique, like pomodoro (but there are probably others) and keep at least one project going.

Most importantly, good luck, and keep going. If you find things getting worse it's a really good idea to see a doctor. Depression sucks, and sometimes the worse it is the harder it is to treat.