Stroke is associated with obstructive sleep apnea.Obstructive sleep apnea is associated with problems in daytime functioning, such as daytime sleepiness, motor vehicle crashes, psychological problems, decreased cognitive functioning, and reduced quality of life. Other associated problems include cerebrovascular diseases (hypertension, coronary artery disease, and stroke) and diabetes. These problems could be, at least in part, caused by risk factors of OSA. Central sleep apnea
In pure central sleep apnea or Cheyne–Stokes respiration, the brains respiratory control centers are imbalanced during sleep. Blood levels of carbon dioxide, and the neurological feedback mechanism that monitors them, do not react quickly enough to maintain an even respiratory rate, with the entire system cycling between apnea and tachypnea, even during wakefulness. The sleeper stops breathing and then starts again. There is no effort made to breathe during the pause in breathing: there are no chest movements and no struggling. After the episode of apnea, breathing may be faster (tachypnea) for a period of time, a compensatory mechanism to blow off retained waste gases and absorb more oxygen. While sleeping, a normal individual is "at rest" as far as cardiovascular workload is concerned. Breathing is regular in a healthy person during sleep, and oxygen levels and carbon dioxide levels in the bloodstream stay fairly constant. Any sudden drop in oxygen or excess of carbon dioxide (even if tiny) strongly stimulates the brains respiratory centers to breathe. In any person, hypoxia and hypercapnia have certain common effects on the body.
Sadness is an emotional pain associated with, or characterized by, feelings of disadvantage, loss, despair, grief, helplessness, disappointment and sorrow. An individual experiencing sadness may become quiet or lethargic, and withdraw themselves from others. An example of severe sadness is depression, a mood which can be brought on by major depressive disorder or persistent depressive disorder. Crying can be an indication of sadness.Sadness is one of the six basic emotions described by Paul Ekman, along with happiness, anger, surprise, fear, and disgust. : 271–4

Childhood
Sadness is a common experience in childhood. Sometimes, sadness can lead to depression. Some families may have a (conscious or unconscious) rule that sadness is "not allowed", but Robin Skynner has suggested that this may cause problems, arguing that with sadness "screened off", people can become shallow and manic. : 33, 36  Pediatrician T. Berry Brazelton suggests that acknowledging sadness can make it easier for families to address more serious emotional problems. : 46, 48 Sadness is part of the normal process of the child separating from an early symbiosis with the mother and becoming more independent. Every time a child separates a little more, he or she will have to cope with a small loss. If the mother cannot allow the minor distress involved, the child may never learn how to deal with sadness by themselves.