I've been unable to concentrate, have short term memory loss and have felt extremely depressed.. And my ability to deal with stress is practically non-existent, leading to other health issues which are embarrassing and uncomfortable, if the previousls mentioned weren't crippling enough.
It turns out that I have vitamin D deficiency (still waiting to have the details from the doc). I live in Berlin, which is far sunnier than where I have spent most of my time in Germany (around Flensburg).
It's 2019 now, so reading the Internet will tell you e.g. Rickets in American children increased by about 300% when they removed all the added vitamin D to their diets back then, which is why milk became fortified.
That vitamin D can cause a host of issues including death. If you are dark skinned, you will have it worse - a study in the US showed that black Americans on average had about a 4th of the vitamin D levels that white Americans had in their blood, which was basically the threshold at which people were depressed/happy.
That 80% of your vitamin D comes from your skin, only 20% from your food, the most of which you can absorb at around 50% when had with fat and less than half that if you don't.
That it's not as simple as going out into the sun for hours at a time, but in short doses multiple times a week.
I live in Berlin and have olive skin. Over the many years of living here, my skin has gotten lighter and I can no longer tan as dark as I could - I can actually get sunburnt if I return to a sunny place and sit in the sun for too long.
My diet is pretty healthy - although I have avoided eggs (especially the yellow) and somehow stopped having milk over the past couple of years, I eat bio meat most days of the week.
I am looking at a dietary reform and psychological therapy - pretty convinced that the deficiency is the culprit for the other problems by body has been having a hard time fending off.
My advice: if you have a vitamin D deficiency, don't ignore it. It plays out as stress, sadness, tiredness, forgetfulness, insomnia, etc, etc. All things that tend to creep up on you in everyday life and your first reaction is to dismiss it as something else (maybe itstress at work? Maybe warm weather? Maybe allergies?), things you think are temporary but that also create a devil's cycle. (Lack of sleep = more stress = loss of appetite = depression = lack of sleep =...) The longer you deal with it, the longer you are at risk to have other ailments from a weakened immune system.
Just wanted to post here since TT is still a top result for this topic - wanted to let people know that there is hope so go to the doctor and start fixing your issues one at a time.