"Sinking" is about coping with depression. When I was 18 years old I fell into deep depression. It was one of the toughest moments of my life. Everything felt hopeless and there was no way to feel better.
I remember people mistakenly believing that being depressed was my choice, that I just had to "snap out of it.” But as like any other mental illness I couldn't simply decide to stop feeling depressed.
It was like constant being pulled down from the surface and not being able to float.