This sounds like some version of ergot poisoning, or possibly a related toxicity from another similar fungus. Ergot caused a wide variety of neurological conditions, and is often cited as the cause for the Salem witch trials. In ancient societies, this was a common toxicity. There are potentiators that interact with ergot at lower doses to ...
You describe iodine deficiency.
Health Consequences of Iodine deficiency
Iodine Deficiency Disorders (IDD) are one of the biggest worldwide
public health problem of today. Their effect is hidden and profoundly
affects the quality of human life. Iodine deficiency occurs when the
soil is poor in iodine, causing a low concentration in food products
Heavy metal poisoning — a mixture of lead, arsenic, mercury, manganese, and maybe a few others should be enough to produce these effects..
Manganese poisoning can cause mental health problems, including hallucinations.
Mercury poisoning can cause lethargy.
Chronic lead and arsenic poisoning can lead to a number of health problems, such as high blood pressure ...
The Solanacea are a variety of similar plants, many of them are used as food, including tomatoes, potatoes, bell peppers and chilli peppers. Tomatoes, and many solanaceaes, are rich in vitamin C.
Among them, there is also unedible plants with mild neurotoxins, like the tobacco, which contains nicotine.
However, some solanaceae are very poisonous, ...
I find myself wondering whether some source of low to medium intensity generally pervasive environmental microwave levels could be a candidate.
Microwaves are non-ionising (low energy) radiation, that transfer as heat and elevated kinetic energy, upon interacting with water and fats and a few other things (which is why we use them ...
Mild milk sickness
Milk sickness produces both listlessness and insanity, although I'm not sure if it causes infertility. It also causes sensitivity to light, which would go along with the bog environment they live in.
However, large (or even medium) doses of it are very deadly.
Therefore, you could do a little handwaving to produce another (seemingly) ...