It has to be a habit, you must have noticed this. Lack of energy is a good justification to spend the least that you can and it can be tempting to sacrifice physical activity in such state, but I have the impression that as an exception it's worth ignoring instincts and moving anyway, because the less you demand from the body, the clearer the signal that it can afford the torpor.
The intuition side of things can be challenging here.
There are times when I don't feel acutely like exercising but I have the energy for it, and those times I feel hugely positive for doing it. Other times I have felt completely depleted and in those states I often end up worse off. I'm finding very small amounts of vitamin D (along with varied diet that includes vit A and K from food) keeps me in a state to always have energy. Just 1kiu or 2k every othet day. I completely stopped exercising when I ****88 my sleep and health from lifting / running and feared exercise for such a long time after that. Added to a period of forced eating and probably prolonged vit d deficiency I absolutely ruined my liver health. Exercise when in the above state is the only thing that is truly helping. Liver flushes had some positive impact also but I think they can bring about problems of their own.
Walking, unless on my feet for a good chunk of the day, doesn't cut it for me. It also feels aimless after a while.
I think lymph stimulation is key when it comes to shorter exercise. Personally I find I enjoy sprints (not all out though) some slower runs, then "bouncing" type stuff at home like star jumps or spot running or general stuff along those lines maybe with some goblet squats mixed in.
Resolving insulin resistance is key as if you're tanking your thyroid every tine you eat through poor insulin response then you're going to have poor digestion and endotoxin, especially with the most insulin provoking foods.