Is this the reason for hair falling out ?

Yes, you can temporarily lose hair due to stress or a traumatic event such as a death in the family, etc. This kind of hair loss usually grows back.You do lose hair every day due to natural shedding. If you have long hair it may seem like more is falling out.
If you notice thin patches or circles you must go to a doctor and have it checked out. A dermatologist or a general M.D. can give you some tests to find out what is causing it. It could be a problem with your thyroid, anemia, or a hormonal imbalance. Birth control pills can cause your hair to fall out when you stop taking them or start a different kind. It takes a long time for it to start to regrow. At least four months.
It could be due to age. Everyones hair thins as we get older.Giving birth causes it too. After giving birth many women have hair loss as there hormones go back to normal.