Hydration is important, as are a million other things. Sleep? Stress? Overall health? What about menopause/hormonal changes?
I find if I am tired during the day, going out for a short, 15-30 minute walk helps. How much do you exercise outside, all year round?
Rule out the physical first. Then look at nutrition, hydration, amount and type of exercise, and rest. We need more recovery as we age. That doesn't mean being a couch potato, but it does mean good quality sleep and active recovery from hard efforts at sports.