If you`re experiencing this I suggest you seek a medical diagnosis.
This is one reason that is explained in the following video.
Telogen effluvium can be acute or chronic. If there is some "shock to the system", as many as 70% of the scalp hairs are then shed in large numbers about 2 months after the "shock". This
sudden increase in hair loss, usually described as the hair coming out in handfuls, is acute telogen effluvium.
Have you more information about your situation? Any pictures you could add?