So hard to say in abstract without knowing more. I always wonder if this is something you can fix through process and habits, or if this is something you just need to feel intensely first, and only then will the right behaviors will emerge.

For example, if you're feeling comfortable and handsomely compensated at your current job, and you have the sense of security that you'll keep being hired forever, why would you burn the midnight oil and go the extra mile? Is your lifestyle going to change at all if you get to that next level? You might work longer hours, experience more anxiety and stress, and get barely any upside in return.

My hunch is that the human brain is efficient. It won't make you work any harder than you need to if you have obtained the thing you already want.

Maybe the real question here is whether you truly desire to be this aspirational high-performer, or if that's an idea you're romanticizing, something you feel you should aspire to, but you don't genuinely crave it. You end up fighting between the idealized you and the practical you. Which may explain why you're burning out and losing steam eventually, you can only force yourself to do something you don't feel like doing for so long before the body rebels.