It was 4am and Alexandra Wenman was in a B&B high up in the mountains of Cusco, Peru , 11,000 feet above sea level. Since arriving the day before, she had been suffering from altitude sickness , feeling dizzy and nauseous. “I woke up in the early hours feeling terrible and I searched in my bag for my rainbow obsidian. I carry crystals everywhere,” says Alexandra, 47, from Tottenham, north London. “I’d brought this crystal because it’s a grounding stone, it pulls you back to earth. I knew that