Here are some of the symptoms from medline:
Difficulty breathing
Wheezing
Abnormal (high-pitched) breathing sounds
Confusion
Slurred speech
Rapid or weak pulse
Blueness of the skin (cyanosis), including the lips or nail beds
Fainting, light-headedness, dizziness
Hives and generalized itching
Anxiety
Sensation of feeling the heart beat (palpitations)
Nausea, vomiting
Diarrhea
Abdominal pain or cramping
Skin redness
Nasal congestion
Cough
In my experience, Some of these are quite late in the process. Early signs include the hives, anxiety (due to hypoxia), palpitations, hives or skin redness, feeling of tightening of the throat.