We refer to physiological alopecia as telogen effluvium in medicine. On a normal scalp, about 1/3 of the hair is in the growing phase, 1/3 is in the resting phase, and the other 1/3 is in the shedding phase, and yet, in some cases, all hair follicles synchronize, and they all enter the shedding phase. This shedding phase is temporary, and results in temporary hair loss.
This is most commonly seen in mothers a few months after giving birth. Also, when someone experiences an illness with high fever, has a major injury when the body is in remission or after strict diets or severe emotional stress, telogen effluvium can occur.
If the body is otherwise healthy, if anemia or any thyroid diseases are not present, physiological alopecia lasts for a couple of months, and the hair grows back afterwards.
The important point here is to identify if the cause is physiological or if there is an underlying disease, and determine the treatment accordingly.