Zebra Danio laying on gravel

This zebra danio has been laying on the gravel and in the plants lately.
I've had one danio that's often not with the others and I think this is it.

We've had it for about 20 months, not sure how old it was when we got it, but it seems it's life is coming to an end.

Anyone have an idea what's going on with it?
Here's a short video I took of it.

 

It may just be very old, or swim bladder disease maybe?

 

I'm thinking old age.
When I got home from work I couldn't find it.
Had to dig through the plants for 10 minutes get it to come out, and then it started swimming like that.

I caught it and put it in a specimen container to observe it, and it ended up laying upside down on the bottom.

 

I have seen a few threads places where it discusses fish seizures. Maybe something to consider. I don’t believe they found a treatment though.

 

This went on for quite some time, until the danio exhausted itself and just laid in the plants.

Once rested it started again.
Rightly or wrongly, I opted to put the fish out of its apparent misery and euthanized it with clove oil.

After passing, blood came out of it's gills, so something was definitely going wrong with it.

 

I'm sorry for your loss. That behavior did look rather severe, I'm not sure there would have been any treatment for it.