Have a look at your diet. Since my late 40s I would get really really tired, especially in the afternoon after lunch. Siestas are great but not when you are at work
I found that for me at least, carbohydrates send me to sleep! I have changed my diet (12 months now) and have eliminated bread, pasta, starchy vegies and really restrict my carbs, drink lots of water etc. I have much more energy now, rarely need to have a daytime nap and have lost almost 70lb into the bargain. I dont know why the carb effect was so much more pronounced the older I got but it certainly was! I am on HRT and that, combined with the diet have made me way way way less anxious and depressed over this past year!