I remember a long time ago I was so overwhelmed by this feeling of depression - no point in anything to be found.
So I laid down on the couch, staring in the dark, hardly moved my body or thoughts, just sunken in darkness. And stayed there for a couple of days (? can't remember how long exactly).
Feeling that bad, well, it sure gave me something in return - all responsibilities gone, nothing to do or not to do, no caring for me or others, just not able to do it.
I sank to the bottom of this 'state of mind', laying on the couch, not eating, phone and doorbell ringing - I didn't answer, just staring in the dark (even in daytime)
Suddenly, unexpectedly - I 'popped out'. Full of life, sparkling of joy. There was no trigger, it just happened.