Afaik, both. Like a lot of shit things—they are caused by depression, and they cause depression, horrible reinforcing loop. While the effect of bad health on sleep is obvious, you can also see this work in reverse; e.g. temporary severe sleep restriction has an anti-depressive effect. Notable, though with not many useful clinical applications, as constant sleep deprivation is also really unhealthy.
Afaik, both. Like a lot of shit things—they are caused by depression, and they cause depression, horrible reinforcing loop. While the effect of bad health on sleep is obvious, you can also see this work in reverse; e.g. temporary severe sleep restriction has an anti-depressive effect. Notable, though with not many useful clinical applications, as constant sleep deprivation is also really unhealthy.