" The bodies state of red alert brings about a series of psychological changes, driven by gathering tides of adrenaline or cortisol. These are the fight or flight hormones, which act to help and organism respond to external stresses. But when a stress is chronic not acute, when it persists for years and is caused by something that cannot be outrun, then these biochemical alterations wreak havoc on the body. Lonely people are restless sleepers and experience a reduction in the restorative function of sleep. Loneliness drives up blood pressure, accelerates ageing, weakens the immune system and acts as a precursor to cognitive decline. According to a 2010 study, "Loneliness predicts increased morbidity and mortality". Which is an elegant way of saying that loneliness can prove fatal. "

― Olivia Laing , The Lonely City: Adventures in the Art of Being Alone