Too much work.responsibilities and goals.

I think there are two ways to tackle this. The first is to find the things that energize you, which can either be something you find inspiring, like a song or a story or a friend, or something you hate, like someone who insulted you. The other way I find more reliable but ymmv, you look at the pile of work ahead of you, and you essentially give up any hope of finishing it and getting to relax. There is no longer anything to look forward to, you exist to do the task and it no longer matters whether you're happy or not, the task is the one and only thing. When you're done with that task, there will be another task, and so on forever. That kind of hope crushing mindset actually let's you slog away, and typically you'll be surprised how quickly you'll finish