Depression
One of the most difficult and scary health conditions is major depressive disorder, or MDD. It is characterized by someone being in a constant low mood and showing absolutely no interest in daily activities.
An MDD diagnosis would require five of the most relevant symptoms for a minimum of two weeks, and these symptoms are: depressed mood, anhedonia (which is the loss of interest in activities that were pleasurable before), fatigue, poor decision-making, sleep problems, terrible concentration, appetite changes, restlessness, rapid-talking, pacing.
There are many factors that could make depression more likely, such as chronic stress, bad mood regulation in the brain, a history of prolonged trauma, substance abuse, unhealthy nutrition, unresolved grief, various personality traits, being a female, and genetics.