sleeping in the litter box

My Sphynx girl is 15.  She has asthma, and she takes prednisone every other day for it.  She has had problems with the litter box sometimes where she doesn't go in the box or she just poops where she walks, and the vet said that is from arthritis in her back and legs.  I started her on Dasuquen last night.  Today she's been sleeping in the litter box.  She has never done that before today.  Hubs said she was in there, and I pulled her out and put up the gate.  She got through the gate and layed back down in the litter box.  Hubs then removed her again and now she's sitting on my lap.  

What would cause this?  It's so odd.  

I know cats will occasionally sleep in the litterbox, but it is unusual. Is the box cooler or in a cool room? I'm just thinking she's trying to get out of the heat. Or maybe the litter just feels soft to her perhaps?

The litter box is where her scent is the strongest and therefore is clearly marked as her "territory". 

As a result, cats might stay in the box because it is where they feel safest. I would assess the situation to see if there is any thing that has changed in the household that makes her feel unsafe or anxious.

If you believe the meds is the only change in her life since the incident occurred, I would consider having a conversation with your Vet to understand the side effects. May be there is something there that caused the issue. 

If she doesn't have to take it regularly, perhaps try to skip the meds for a few days and see if it makes a difference.