You guys won't believe this, this is great but REALLY weird. Timmy is alive

My sister just called me and said this morning after she found him upside down with all his legs just hanging limp that she took him out to make sure he was dead and he was completely limp, so she put him in a box in the backyard until my brother in law got home from work so they could bury him next to the pond. Get this, she said they opened the box so she could see him one last time and when they did he was staring at them

He's alive and back inside huddeled up next to his heater right now. My Niece was so happy she started crying again lol.
What the heck is going on though?? Has anyone ever heard of a turtle doing this where he's completely limp like that? because my sister says she swears he was dead.
As to the tank size I was mistaken about the 20l, that was actually a 29g, but even at that just last week I was talking to her about getting her a 40b for him. We'll make sure he's doing okay and if so then I'll look into getting a 40b for her.