There are many types of depression,
Reactive depression which happens when life throws you a blow,
Clinical depression can be serious, many causes, but this is a depression where some sufferers cannot get out of bed, doesn't bathe, doesn't eat, can be unaware of what is going on around them
Bi polar or manic depression is very serious, often leads to suicide when a low strikes but when a high strikes this too can cause harm, promiscuity, burns up energy but doesn't need sleep, thrills such as shop lifting .
No, I am not an expert, I had to attend meetings with a psychologist when I worked at the drop in centre