A Sudden loss of hair is not normal. This is called Telogen Effluvium. This is a disturbance in the hair follicle and can be reversed and possibly prevented in the future. This temporary hair loss usually happens after stress, sudden weight loss, surgery, certain medications, traumatic event or childbirth.
Treatment options might be as simple as a topical vitamin or a hair growth shampoo that will make your hair grow stronger and longer faster.
I use a Capilliscope to look into the hair follicle to see what is happening so I can make a proper recommendation on what you need to grow ALL your hair back. Your hair is the last thing you need to worry about...Right??