Is my snake lethargic and becoming sick? Help.

[pet_owner_Lanee16]

I recently received a corn snake from an owner who didn't want it. I put it in a 20 gallon tank with a substrate of peat moss. I has a driftwood center piece that it likes to climb on and plants. It's been with me for about a month, eating regularly thawed pinkie mice once a week. The temp stays slightly under 80 degrees with a heating pad on one of the walls.
Last night, I noticed it coiled up under a cavity of wood. I went to check on it, and its reaction startled me. It's head moved, but it didn't flinch at any touch. I was worried that it had become dehydrated and something was wrong with the water so I replaced it. When I returned the clean water bowl to the tank my corn snake began to drink lots of the water. It then slithered away. Thinking the situation was resolved, I went to bed.
In the morning I found it in the same, if not worse state. It didn't flinch nor move away from my hand. I became more worried at the fact that he wasn't testing the air. I began reserching and found a list of symtoms to snake sickness. One was loss of apitite. I wanted to test if my snake would take a pinkie mouse to see if I could put together possibilities for it's behavior.
He did snatch the mouse, and became active for about 2hours. Slithering and climbing and returning to an active state of testing the air with it's tongue and such. But as time passes, he went to the heating pad and coiled up again. I figured this would be normal for digestion, but my snake started to not react to my movement or sound. There was occasional flicks with it's tongue, but I would say it is acting lethargic.
There are no other symptoms pointing to sickness. No discharge from the nose, no visible mites, and my snake isn't opening its mouth or gasping for air. Besides being VERY inactive, everything seems fine. I have considered that the snake could be constipated because I haven't seen feces, but I thought that this could be because of the insects in the tank that could potentially consume it, or it being soaked up by peat moss/Coco fiber sunstrate, and the fact that it ate immediately when I gave it food.
Is this normal? I am wondering if it is on the verge to shedding, but it isn't aggressive and it ate the pinkie mouse I gave it. (Even taking this photo, it wouldn't flick it's tongue and its becoming worry some)

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[Karl_Mcknight]

What concerns me the most is the temp.

First of all, a snake needs warmth to digest food. If the temperature is not right, it may get sick, and the snake may even refuse to eat.

You stated in your post that you had a heat mat attached to one of the "Walls." and you stated the temp was under 80 degrees. Since your snake crawls on its belly along the floor of the cage, what good does a heated wall do? The heat mat should be on the bottom of the cage, and a Hiding Spot for the snake should be directly over top of it.

You should measure the temperature "Inside of the Hiding Spot" and the temp should be between 83 and 87 degrees. (Many of us opt for an 85 degree warm spot.)

Then you should have another hiding spot on the unheated end of the cage. The temperature inside of the cool hide should be about 72 to 75.

I'm going to guess that your snake is probably uncomfortable because the cage is too cool.

 

[DollysMom]

Snakes sleep a lot. You may just have caught the snake sleeping. Besides Karl’s good advice, my concern is a lack of hides. Snakes need to hide. My snakes spend 90% of their time in their hides. This is normal behavior. Also, peat is not the best choice of substrate. Do you have a hygrometer? Have you checked the humidity? 40 to 60% is the range to aim for. Best wishes.