What could cause someone with chronic fatigue to feel great and energetic starting at 11 pm?

Get yourself a complete health test.

If there is no chronic cause, then it must because of your breathing.

It could because of your breathing, it happens as you are breathing less every day so it must be causing fatigue, you must be having sinus or deviated nasal septum which is making you breathe less.

Once your body gets warm or later in the day you will get better.

So read my other answers if it is chronic or has been there for more than six months for a holistic solution.

Please read below on how to take care of DNS, Sinus etc. which is causing you to fatigue or breathe less.

Off late i also found something called Salt room therapy. While relaxing in one of treatment rooms, customers inhale the dry, salt-enriched air deep down into the lungs, where the healing benefits do their greatest healing. The salt loosens the mucus, which begins to clear quickly, and inflammation is reduced, which makes more room in the airways for you to breathe. Symptoms subside, sometimes for up to 12 months.

Dry salt air is more powerful than moist air. The negatively charged ions in salt improve our health and mood. Inhaling particles may reduce inflammation and mucus in the lungs, improving most respiratory conditions such as asthma, allergies, bronchitis, sinus congestion and Chronic Obstructive Pulmonary Disease (COPD).

See if you have it nearby or see if you can customize, like use a nebulizer at home. BUT MAKE SURE YOU KNOW HOW TO PREPARE THE RIGHT SALT WATER OR SALINE SOLUTION. PLUS ENSURE ITS HYGENIC AND YOU HAVE CONSULTED A DOCTOR WHILE CUSTOMIZING YOUR SALT ROOM THERAPY USING A NEBULIZER AT HOME

If its what Syed says then ..

With Balloon Sinuplasty, there is no cutting of nasal bone or tissue. With Balloon Sinuplasty, ENT doctors open inflamed sinuses in the same way that heart surgeons open up blocked arteries during balloon angioplasty. The procedure is less invasive than traditional sinus surgery, and effective at relieving symptoms of chronic sinusitis. Balloon Sinuplasty allows patients to return to normal activities quickly. Unlike conventional sinus surgery, it does not include removal of bone or tissue from the nose. And, Balloon Sinuplasty is now offered by some doctors in their office under local anesthesia, so that there is no need to go to an operating room or undergo general anesthesia.

While recovery time varies with each patient, recovery is typically fast. In a study of in-office balloon dilation, most patients returned to work and normal activity within 2 days.

However, even I am suffering the same since childhood, though in my case it is just moderate.

Again, in my experience, I have also seen patients find no relief in Sinoplasty but still its far better and you get immediate relief to a major extent in most cases.

See its like this there are chances you will get completely cured or in case the symptoms might return as well.

Its just sometimes you are body is susceptible to DNS.

So, in the long run if you have the time and patience and believe in holistic healing, then I would suggest you go for Yoga and practice breathing excercise also called Pranayam.

Some of them are alternative nostril breathing (AnilomVilom) and Kapalabhati. With these techniques you can surely get cured of your DNS but it will take around 6 months to 1 year. But life long you will be cured. You just have to find a right Yoga Guru and you have to increase the intensity of the breathing excercise as you start.

Also Neti Pot ( Please Google -Nasal irrigation), is excellent. It hardly takes 5 minutes everyday. It might be hard in the beginning but don't give up. Surely, if you get a Good Yoga Teacher he can help you in 3-6 months time.

This is my experience. Now I am just doing Neti Poti and I am fine but I have to do it religiously without missing.