In normal terms, hair growth has 3 phases,
At any given time, hair will be in any one of the phase.
1. Growth phase
2. Resting phase
3. Shredding phase.
When the a large number of hair is in Shredding phase, you will have hair fall, noticeable.
But it's a passing phenomenon.
But if the hair fall is more, that indicates something is wrong, such as nutritional or hormonal imbalance or genetic or some external cause.
Start eating good & nutritious food containing necessary vitamins & mineral.
Do regular exercise
Keep your scalp & hair clean.
Don't use harsh shampoo.
If the hair falling is sever, consult in person