We have learned of differences between the laws of a nidda and a zava (see daf 36).
As we have learned, according to Biblical law, when a woman experiences her menstrual cycle she is a nidda whether she bleeds only once or many times over a period of seven days. At the end of seven days she immerses in a mikva and is rendered ritually pure. The eleven days that follow are called yemei ziva. If she experiences vaginal bleeding during that time she is rendered a zava.
The Mishna on today’s daf discusses what the woman’s status is at different times during the month. According to the Mishna, during the eleven days of yemei ziva even if the woman does not examine herself, we do not assume that she bleeds and becomes a zava. Once the time of her period arrives, however, we must assume that she has become a nidda, even if she has not examined herself. Rabbi Meir teaches that if there are extenuating circumstances this may not be true. He rules that:
If a woman was in a hiding place when the time of her regular period arrived and she failed to examine herself she is definitely pure, because fear suspends the flow of blood.
There is some research that suggests that severe depression or psycho-social stressors can affect a woman’s physical health and can lead, in some cases, to amenorrhea – a cessation of a menstrual cycle. While Rabbi Meir’s opinion is brought in the Mishna without any opposition, the commentaries do not accept his ruling, and it appears that the Sages disagree with him on this matter.