Your health depends on how you feel. The argument you’ve just had with your lover has left your blood boiling. You phone a friend, who makes light of it and, before long, you’re laughing. Our emotions have a capacity to harm and heal – not just psychologically but physically. Research has shown that having to deliver a speech can double the severity of allergy symptoms for two days, while crying is soothing because stress hormones are carried out of your body in tears.