Mast Cell Activation Syndrome (MCAS). This is what happens when mast cells aren’t working properly. For some reason (not yet known) these cells are releasing chemicals when they shouldn’t, resulting in a list of unpleasant symptoms. Instagram, Fitness, Immune System, Mast Cell Activation Syndrome, Immunology, Mast Cell, Allergic Reaction, Chronic Fatigue Syndrome, Dysautonomia