Poisons can certainly cause confusion and difficulty typing. Metal poisons such as mercury and manganese cause nervous system damage, leading to motor symptoms, as well as harm to the brain. The saying “mad as a hatter” originated because of such poisoning: 19th century hat-makers used mercury salts to make felt from rabbit fur, a process known as “carrotting”.
Curiously, the famous Hatter at Alice in Wonderland’s Mad Tea Party probably did not have mercury poisoning at all: Lewis Carol likely based the character on an eccentric furniture-maker and mathematical lecturer who wore a top hat. Alice’s Hatter shared his eccentric extroversion, with no symptoms of the shaking hands, paranoia, or excessive timidity that characterized the mercury-poisoned hat-makers.
(Drawing of the Hatter from victorianweb.org)