I can do one on depression. But I can't really do an essay :')
Depression is one of the many things that cause people to take their lives or hurt themselves. Its basically a swirl of emotions that you can't handle coming forward at the same time, and one wrong thing can make your entire mood bottom out. It can cause anger outbursts, outbursts in general, self-hatred, self-harm, suicidal thoughts, and constant exhaustion.
Suicidal thoughts can lead to suicidal acts, and self-harm can lead you to the morgue or the hospital. People with depression often don't have the willingness to do the simplest of things - brushing their teeth, hair, changing clothes, eating, drinking, etc. Often, people with depression mask their emotions with a smile, and go on about their day - thoughts running through their head. They're also usually overthinkers, meaning they overthink things - like if someone is messaging you late, you'll think they're not interested or hate you. Its just how the mind works when overthinking things. Depression is caused by many things - trauma, basically anything.
I know this might not have helped, but I tried :)