High levels of acetylcholine (ACh) can cause a toxic condition called cholinergic crisis, which can lead to symptoms like: 

    Muscular: Weakness, paralysis, fasciculations, and involuntary muscle contractions 

Respiratory: Wheezing, shortness of breath, and bronchoconstriction 
Gastrointestinal: Diarrhea, vomiting, abdominal pain, and increased gastrointestinal motility 
Ocular: Blurry vision and miosis 
Cardiac: Bradycardia and hypotension 
Neurological: Headache, insomnia, confusion, and giddiness 
Other: Increased sweating and salivation, frequent urination, and tightness in the chest 

In severe cases, cholinergic crisis can lead to central depression, coma, convulsions, slurred speech, and respiratory depression. Death can occur due to effects on the brain, heart, and respiration. 
The venom of a black widow spider can also cause a dramatic increase in ACh levels, leading to severe muscle contractions, spasms, and paralysis. 
The body requires choline to produce adequate levels of ACh. Choline is a building block of ACh and is necessary for proper brain and nervous system function.