Undulated trigger always on its side?

[justoomuch]

I have recieved this trigger with a tank, (trigger was a bonus, i guess) He is fairly tame for one of these boys, but he seems to sleeping all the time! whe it's feeding time he darts up, eats, runs around a bit like normal, then goes back in a liverock cave and lays on a 45 degree angle or flat down horizontal....

He has no other sympotms, (eyes, breathing, fins are perfect, mouth normal) and the water is good...

Damsel in the tank he came with, (still is) and it runs around all the time... Is this normal? Apparently the trigger has been doing this for some time before i got him

p.S. I recently heard it might be the substrate, and to replace that with new livesand...

When the previous owner received the tank, the rock was covered in red algae, 2 protein skimmers and extra filters later, everything has cleared up... is the liverock OK? Damaged?