My hair is rapidly falling out. I've got test for a lot of things but it came out negative? What's going on?

Telogen Effluvium. Telogen effluvium is a form of nonscarring alopecia characterized by diffuse hair shedding, often with an acute onset. A chronic form with a more insidious onset and a longer duration also exists. Telogen effluvium is a reactive process caused by a metabolic or hormonal stress or by medications. Generally, recovery is spontaneous and occurs within 6 months or longer. B12 shots are helpful.