This condition is called Telogen Effluvium. It's a reversible condition in which hair falls out after a stressful experience.
The stress pushes large numbers of hair follicles into a resting phase. Within a few months, those hairs can fall out. Types of stress can include any hormonal issues like
thyroid. It's a reversible condition but needs to b treated to prevent further hair loss. Dandruff can also aggravate the issue of hair loss.Consult a Dermatologist to prevent further progression of the same.