I don't think it is an energy problem either. I can find energy for other things, just not my employment.

I think people were right that I am stagnating and I feel the need for new challenges.

The catch 22 is that my job is so amazing that it gives me the newfound (newly realized) freedom to see the world while working. So I either stay, find some motivation to avoid the shame of not working, and keep travelling to fulfill my work/life balance.

Or I find a new job with new motivation where I'll be putting in more hours, more commitment and perhaps have less time for travel.

But regarding the energy, I take daily supplements of vitamin D and all the B vitamins, and I do feel that it does help.

With respect to supplements... I can relate to what you describe and I tend to think it's not just based on chemistry. That being said, on different occasions, I felt a dramatic boost when taking magnesium + zinc + B cocktail. I guess it means I was deficient in those. Who know is you aren't...