Severe and sudden hairfall (29F)

I have always had healthy hair with little to no hair fall. But starting last month, my hair is falling out in huge clumps. I counted them, about 200-300 a day. Dandruff was a constant in my life since I sweat a lot but I don't think its the reason for this sudden hair loss. Worried the docs might just push an anti-dandruff regime without going into further details. What all could be the possible reasons for this sudden hair fall ?Please help...