Because I haven't done an RCT, there are potential confounds. Perhaps I'm more likely to reddit (vs go outside) when I'm lower on energy to begin with. And there's a lot of noise, and the metrics are subjective.
Also: relaxing takes some practice. One can sit in a beautiful place with spa music playing and still have one's mind buzzing, so it wouldn't be restorative. Taking a proper mental rest took me years to get good at.
Another caveat: "mental energy" is a metaphor that may not exactly correspond to something physical like neuron ATP levels or whatever. And there are many parts of the brain, and different activities use different subsets, so activities overlap in strange ways. Still, as far as self-cognitive-science goes, I'm relatively confident in this observation.
YMMV I guess, but I'd be surprised if anyone's programming neurons are replenished by memes. Maybe by a nice movie.
Mental faculties are like muscle in that they get tired and need rest. A difference is that it's easy to sense how tired muscles are and hard to sense how tired the mind is.