> No relationships but I'm antisocial to a tremendous degree so there's not much helping me there.

That may be partly the issue. Studies into "happiness at work" often show it's not the work itself that necessarily determines happiness, but the quality of the relationships you have at work. For example, some work that may seem tedious and dull can become quite interesting if you are working on it together with someone you like and respect - and it's even better if you can have a blast with them. On my last gig for example I was doing dreadfully tedious work, but it was made better because several people I worked with were just awesomely nice people and we tried to have some fun too. Perhaps there's someone at work that you can buddy up with, and your manager might be able to help you there.

Having a relationship can be an important factor too - apart from anything it helps you get out of your own head and relax. Do you do any social activities on the weekend? It might be worth joining a cycling club, a running club or even a Crossfit box - you say you like exercise, something where there are other people to talk to. Just being around other people and talking to them will help - I know this is like hell on Earth if you are basically shy, so this is something you are going to have to ease into gently and get support if you need it - it will get easier.

Having said all that this is a difficult thing to diagnose and remedy via HN! As mentioned before you might find it worth talking to a career coach or perhaps even a counsellor. Feel free to email me if you want.

Have you never done it before? It's intimidating walking through the door, but you'll rapidly discover that there's nothing terrifying about it. Professionals are really good at talking to you about your concerns. You might get lucky and find that your problems stem from the kind of anxiety that dissipates if you can just have someone guide you through venting it fully and clearly in a venue where nobody is judging you.