The mandarin's behavior sounds in the range of normal. Mandarins can actually appear kind of freaky when they sleep. They cover themselves with a little mucus as a protective mechanism and the first time I discovered mine in its sleeping spot, I was positive I was looking at a dead fish.

So I can't let this go without commenting...even with plenty of rocks and pods, your tank can only hold 8 g worth of rocks and pods, which may not last your little guy long. Please start reading up on how to train a mandarin to accept frozen foods and also try some methods to encourage increased pod populations, just to give this beautiful fish the best possible chances. Don't be shy about asking questions. We are all here to help.