How do i stop my hair falling out?

Depends on cause...: One's primary care doctor can check for medical causes. If none are found, then one can see a dermatologist, especially one specializing in hair restoration (some treatments: minoxidil, finasteride, hair transplants...) Medical causes may include: hormonal problems (low thyroid), seborrhea, alopecia areata, stressful illness. Other causes: genetic male/female pattern baldness, telogen effluvium...

Medical Reason?: The best answer would be to explore if there is a medical reason why this is happening to your (e.g. thyroid disorder). Talk to your regular doctor, if they cannot find an answer, then talking to a dermatologist is always appropriate as well.