A 'massively underdiagnosed' condition can cause a long list of nasty symptoms, including breathlessness and pain all over the body, according to an NHS GP. Dr Ahmed, who shares educational videos online as @Dra_says, explained the symptoms that can be associated with Mast Cell Activation Syndrome (MCAS) in a recent post. As per NHS research, MCAS is a condition that 'causes severe allergic symptoms. The symptoms of MCAS range from severe itching and swellings to full-blown allergic reactions (