Metaphors for depression I have used

A badly-trained border collie who needs constant attention and toys to chew on, otherwise it starts ripping up the furniture

A large gelatinous blob that I’m trying to hold close to my chest, but it’s slimy and keeps oozing out of my arms and I keep trying to pull the strands back up but they stretch and glop down to the ground like melted cheese

Similarly, a huge bundle of parcels I’m trying to carry gracefully, but boxes keep falling, and as I bend down to pick those up others fall

An unhelpful housemate who doesn’t do anything particularly malicious, but just makes life difficult for everyone else by not doing anything at all

Chronic pain, but chronic mental pain

Building a house on the wall of a cliff, held on by beams and joists that have to be constantly maintained and replaced, or else my house will fall into the sea

Similarly, a recurring infestation of treatment-resistant termites slowly chewing away at my house. I can quell the termites temporarily, and I can repair the house, but I just don’t know when my foot’s going to go through the stairs

A vampire who must stop to obsessively count the scattered rice or untie all the string they come across, except my errant spirit obsessively numbers faults and picks apart situations