Are you eating adequately? If you undereat then probably lack of energy can be attributed to low food intake. A bottle of orange juice is a quick source of energy thats why you feel better when you have it. Make sure you eat enough to maintain body strength and get some fresh air by staying outdoors. Sleep well to recover from the daily stress. Frequent rest periods are helpful in staying energetic as you are a senior citizen. Stay active and have small frequent meals to aid digestion. Make sure to eat enough carbohydrates to stay energetic. Complex carbohydrates are a better option than simple carbohydrates as simple sugars serve as a quick source of energy but do not help to maintain energy levels and cause a sudden rise in blood glucose which is not good for diabetes also. Complex carbohydrates from whole grains, fruits instead of juices, vegetables as raw salads help to stabilise blood glucose and prevent blood sugar spikes. So if you don t have any dental problem, then prefer having an orange as a source of energy rather than orange juice. Hope this answers your query.