I've struggled with low "energy" for decades now (mainly of the mental/emotional kind). I've tried hundreds of things to try to boost it, over the years, with very very few things actually working. I think it's a tremendously complex thing/topic, and until science/medicine fully understands it properly it will continue to elude most attempts at resolution. But thats not to say that your energy levels can't be boosted, but its usually by things which we don't understand &/or can't reliably duplicate. And everybody's different, which even further complicates matters!. For instance, a person is in a "certain type" of low-energy state, and just for that situation their energy is boosted by being around people. But the very next day, even with seemingly the same type of low-energy, their energy is not boosted by being around people (even if its the same people, & the same things happening)!
So, in summary, with a small number of exceptions, i believe that there are a number of factors (ie not just one thing) involved in the ability to increase the "energy" level. Exactly what these factors are ... well that one's for someone else to tackle! lol