Hi Sudden onset of hair loss can be related to recent viral fevers or severe stress, recovery from crash diets etc.this condition is called acute telogen effluvium. I Please eat lots of protein and vegetables in your diet. Use aid ph balanced sulphate free shampoo. Avoid blow drying and oil massages. Get your thyroid levels checked. If you are a vegetarian get Vit B12 and d3 also checked. You may need to take multivitamins supplements for a short while. This condition is usually self limiting as in it will respond even without treatment. However if you see bald patches or significant thinning please contact a dermatologist. Remember in hair loss prevention is always better than cure