A sucking void... that's how I would describe it.
Sucks all emotion, happiness, strength and wellness. It makes me less able to consider those around me, less able to stay motivated, less confident, less concerned about my personal health and wellbeing, less able to care about important things like money or turning up for a job.
I felt soulless when I used to have it.
Now I keep myself on track and haven't gone back on antidepressants for 3 years (despite being on them on and off for 10 years of my life).