I get that way too when I've overdone it. I get gloomy.I think I have done too much. Usually, when I am tired, I don't feel positive feelings so much. But the thing is, I don't feel tired. Maybe I am overdriving...
I do sometimes wonder if taking Calcitriol would help you. It's the final version of Vitamin D but there is the risk of raising Calcium levels too high on it. Also it has a very short half life so has to be taken several times each day.Yes, that's why this thread exists: UV index above 3. For one, human body synthesizes vitamin D only when UVI is above 3. But who knows what other things sunshine does above UVI 3...
This site: https://www.drugs.com/mtm/calcitriol.html says, "Calcitriol is used to treat hyperparathyroidism (overactive parathyroid glands)"
Have you ever been checked for that, @Johannes?
This site talks more about it including symptoms:
Maybe something to ask your doctor about.