He will most likely stop eating, stop coming out of his hide, some just stay in their moist hide even if they are not shedding-but some don't, my leopard just likes to sleep in there and she's perfectly fine but my male, when he gets stressed, he's in moist hide 24/7. Those are just a few signs I know that of. He also might poop on you while your holding him.
When stressed, leopard geckos arre also extremely flighty, and will make a weird croaking/gurgling noise that means you need to put them down before they panic. It isn't completely unusual for your gecko to hide pretty much all the time though. They just feel most secure in tight dark spaces. Also, they are nocturnal, so your gecko is probably roaming around in the wee hours of the morning while you are sleeping away Just give it some time, and your gecko may start coming out to see you during the day, especially if they assosciate you with food!
Lizards also tend to do this thing where they go limp/unresistant and their eyes get a little squinty when they are extremely stressed. Their color may also be dull.
My leo (of two weeks) has always been pretty darn calm. Today I took her out at 9am, I don't ever take her out at this time but my daughter wanted to and she skittered all over our hands so I immediately put her back. Usually she moves slowly and seems calm. Something about the situation she didn't like and I could tell because of how fast she moved as I've been observing her and this was different. I did a lot of google searches on taming etc and everyone says to place your hand in the cage maybe once a day the first week, but don't pick them up so they learn your hand can come in there and nothing bad will happen. Palm up and some say eventually they climb onto you on their own. I'm still waiting for that to happen. Typically I let her climb into the plastic cup I got her and then I let her climb out of it into my hand. I didn't do that today and that may be why she freaked a little.