What are some real word diseases, disorders, drugs, effects, etc. that interfere with a person's thinking-ability (but do not cause blackout)? I am creating a magic system in which I want to create spells that interfere with another person's ability to think clearly. These spells should mimic real world sources of mental impairment. Which is why I have tagged this question as science based.
Some off-the-top-of-my-head examples of inducing mental impairment are nausea from spinning, or poor perception from alcohol poisoning. I am not looking for an exhaustive list of things that can interfere with thinking, but a few examples of chemically induced mental impairment, and a few examples of disease induced mental impairment.
Background of my magic system as extra information:
This is extra information so you can understand why I want to interfere with someone's ability to think.
The magic system I am creating uses willpower, imagination to power spells. So far I have come up with certain abilities; like you can heal wounds, diseases, and regrow limbs if you have a thorough understanding of how the muscles and bones are structured and how a disease works, but not if you don't. So a person's ability to think critically is crucial.
You can also “enchant” things such as shields by willing them to be much more resistant to certain things like fire, but that requires a mixture of a certain magical paste infused with an item related to your desired enchantment, or knowledge of how to restructure the shield's properties. Willing is focusing your attention and imagination onto something, and changing it methodically. Your willpower is based on your upbringing, education and discipline.
So I imagine a scenario where spellcasters battling each other hurl mind altering hexes at each other to disrupt each other's ability to focus, concentrate, remember details, etc.