Chest discomfort and/or pain is a listed symptom of dysautonomia which may have been what you thought was a heart attack.
Conditions such as
Multiple Sclerosis, Parkinson's, Diabetes, alcoholism, Guillian-Barre syndrome, Multiple System Atrophy, and even prolonged bed rest may produce dysautonomia.
Symptoms of dysautonomia are often aggravated by hot weather, unaccustomed exertion, the beginning of menses, large meals, inadequate fluid intake, and stressful situations.