Well, judging by the first post id say 2 things.
First, up the heat to the proper levels- this should stimulate activity.
Second, get a humidity gauge of some sort, even if its a cheapo petco PoS- at least itll give you SOME idea of what youre working with, know what I mean?
Once you know what you're working with, you can decide whether you need to up the humidity or not- if so, take steps to do so.
Are you using a screen top over the 75 gal? If so, your animal is likely HEAVILY dehydrated- mist the cage thoroughly. Hell, mist him anyway- if hes burried in the ground and not moving, he could likely use some rehydration. You seem somewhat savy, so Im guessing you already know that screen tops and aquariums are the equivalent of a giant sponge, that sucks all the moisture right out of your animal.
Not gonna say Im any kind of expert, or that I have tons of experience.
But I did have a young Nile do exactly what youre talking about- dug itself in completely and just sat there. My guess is, she sat there till she felt secure (coulda been hours before she felt secure enough to expose herself), at which point she escaped her cage and I 'found' her the next morning in the tub when I went to take a shower.... lemme tell ya, being naked around a monitor is NOT something Im comfortable with as a male- some parts of the anatomy resembles a dangling food stuff WAY too much.
Needless to say, she had eatten all the pinkys and crickets provided (was quite alot for her size) when I placed her back in her cage, and continued to do so in all the time I had her. Still, she was always extremely flighty, and still is from what I hear.
Provide food. Handle... no... 'be present' as little as possible- give the animal total privacy, if such a thing is possible. Youve only had the animal a few days- its prolly freaking out right now. Give it time, leave it be and let it get used to whats going on- that lil guy was just on one crazy journey no doubt; you gotta give him time to put his lil thoughts back in line before you can expect much from him.
Do those 2 things I said above. Get it onto straight soil- cypress mulch isnt important to it and could be ingested accidentally, leading to all kinds of wonderful, surgery requiring pains.
Think like the animal in this situation- imagine if YOU got dumped in the situation hes in, with the roles reversed; and think about how unimaginably messed up that would be and how terribly stressed it would make you.
Provide proper husbandry. Give it lots of space.
If in 2-3 more days, if youve made all the required changes and youve still seen no movement, you can start really worrying.
