Such conditions happen when the vestibular system and the visual system do not present a synchronized and unified representation of ones body and surroundings.According to sensory conflict theory, the cause of terrestrial motion sickness is the opposite of the cause of space motion sickness. The former occurs when one perceives visually that ones surroundings are relatively immobile while the vestibular system reports that ones body is in motion relative to its surroundings. The latter can occur when the visual system perceives that ones surroundings are in motion while the vestibular system reports relative bodily immobility (as in zero gravity.) Neural mismatch
A variation of the sensory conflict theory is known as neural mismatch, implying a mismatch occurring between ongoing sensory experience and long-term memory rather than between components of the vestibular and visual systems. This theory emphasizes "the limbic system in the integration of sensory information and long-term memory, in the expression of the symptoms of motion sickness, and the impact of anti-motion-sickness drugs and stress hormones on limbic system function. The limbic system may be the neural mismatch center of the brain." Defense against poisoning
It has also been proposed that motion sickness could function as a defense mechanism against neurotoxins. The area postrema in the brain is responsible for inducing vomiting when poisons are detected, and for resolving conflicts between vision and balance.
Premenstrual dysphoric disorder (PMDD) is a severe mood disorder that affects cognitive and physical functions in the week leading up to menstruation. Premenstrual dysphoric disorder is diagnosed with at least one affective, or mood, symptom and at least five physical, mood, and/or behavioral symptoms. Disorders of cycle length
Normal menstrual cycle length is 22–45 days. Amenorrhea is the absence of a menstrual period in a woman of reproductive age. Physiologic states of amenorrhoea are seen during pregnancy and lactation (breastfeeding). Outside of the reproductive years there is absence of menses during childhood and after menopause. Irregular menstruation is where there is variation in menstrual cycle length of more than approximately 8 days for a woman. The term metrorrhagia is often used for irregular menstruation that occurs between the expected menstrual periods. Oligomenorrhea is the medical term for infrequent, often light menstrual periods (intervals exceeding 35 days). Polymenorrhea is the medical term for cycles with intervals of 21 days or fewer. Disorders of flow
Normal menstrual flow length is 3–7 days. Abnormal uterine bleeding (AUB) is a broad term used to describe any disruption in bleeding that involves the volume, duration, and/or regularity of flow. Bleeding may occur frequently or infrequently, and can occur between periods, after sexual intercourse, and after menopause. Bleeding during pregnancy is excluded. Hypomenorrhea is abnormally light menstrual bleeding. Menorrhagia (meno = prolonged, rrhagia = excessive flow/discharge) is an abnormally heavy and prolonged menstrual period. Metrorrhagia is bleeding at irregular times, especially outside the expected intervals of the menstrual cycle.