Your symptoms may be a frequent result of worn-out adrenal glands. Because their hormones regulate the fueling of cells, and especially those of the brain, under-fueling results in low energy and a worn out feeling, sluggishness, trouble getting up in the morning, fatigue and lethargy. Depression is another effect that may occur to an individual with an under-fueled brain and nervous system. 1. Discard or minimize stress factors as much as possible. 2. Eat properly and limit carbs in your diet . 3. Supplement with magnesium citrate powder and malic acid. By doing so, you will strengthen your blood sugar handling system, avoid or overcome fatigue symptoms and lethargy, reduce your risk for numerous health problems and bring about healthy adrenal glands...consult physician for further help

You have start exercising moderately and slowly grow your strength & stamina. I don't think, there is anything wrong with you if all tests are normal. Feeling better after that course may be incidental or psychological. So, have a healthy lifestyle, do exercises moderately, eat healthy food, enough proteins, practise a hobby, play game, if you do so. I am sure this will give you a long term benefit.