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It is hard to say from a photo. But mostly T's die feet downwards & tucked under them, in a ball. Hence the term death curl. Normally when a T is on it's back, it is molting.
Moulting can take anything from a few minutes to many any hours. Just leave them to it. Arachnids have been doing it for several hundred million years & have almost got it sorted now.
T's will often move their legs when molting. But can also lie motionless for hours too.
Moulting so I would not worry but make sure it’s left in peace and the tank got some humidity to help it moult, no food should be left in the tank too.