Cara Delevingne needs to "learn" to relax.The 20-year-old model has walked in dozens of fashion shows this season and is desperate to take a holiday and slow down when her hectic work schedule eases off.She said: "I'm dying. I'm exhausted!"I keep myself going by trying not to drink too much, drinking water and eating healthily."When I've finished fashion week, I want to take a few holidays. I need to learn how to relax."When she does get chance to take time off, Cara loves nothing more than cosying up in her favourite onesies.She said: "I own over 30 and leave a trail of them at my friends' houses."Friends are said to be concerned for the British beauty as they fear her busy work commitments and love of partying could lead to burn out.One pal told Britain's Grazia magazine: "She's got a schedule that only an energy-filled 20 year old could manage."She's loving the job, but some close to her are worried she could burn out."Cara has always been pretty wild, the way she's going she could end up wilder than Kate Moss."