Playing dead?

[FriendsNotFood]

I introduced 2 more shrimp into my tank. One of them looks like it’s playing dead....it swim to the surface of the water, flips itself over, & just lets itself float down. Is this normal?

[Varanus]

When its done floating down does it proceed to walk/swim in a normal way? If so then perhaps it is just not bothering to use the energy to swim down and instead just floats down, but it is unusual.