Common symptoms of high ammonia:

Feeling very tired
or sluggish

Staring or
"zoning out"

Nausea
or vomiting

Losing touch with
reality/hallucinating

Unusually irritable
or uncooperative

Aggression

Lack of appetite

Slurring words

Headache
Symptoms of a urea cycle disorder (UCD) may appear at any time and can vary from person to person. Normal things in life, like being sick, stressed out, and eating foods that are high in protein, can cause ammonia to rise to toxic levels. This can trigger a hyperammonemic crisis. A hyperammonemic crisis is when there are extremely high levels of ammonia in the blood and it requires immediate medical attention. Even mild symptoms can mean that ammonia levels in the body have risen to a high level which can lead to serious health problems if not treated.
Symptoms like these should not be ignored, because they may be signs of high levels of ammonia which can lead to coma or permanent brain damage.