Been there. It really depends on what else is going on in your life and why you have low energy. Assuming you have the basics covered, like good sleep, good food and good water (if you don't, that's likely the problem), and your work-life balance is adequate (this is usually what knocks the rest out of whack for me), then starting super slowly and not pushing it even when you want. Perhaps set a goal that you know you can make, maybe 15 minutes a day?

If you see no improvement at all then definitely mention it to your doctor.

It could be vitamin deficiency. Vitamin D during low sunlight seasons really boosts my energy.