Elderly Gopher - Head Sway and Upside Down

[zoonandes]

I have a 40 year old male gopher snake (caught by my uncle right before I was born 39 years ago).

About 3 months ago I noticed him with his back/neck leaned backwards in his cage. This lasted a few hours.

About 2 months ago I found him upside down in his enclosure and he was not very responsive and presumed he was dying. He had eaten a live mouse (his only diet) a a day or 2 before. After a day or so, he righted himself and was back to normal. Initially I thought that either the mouse was "bad/sickly" or that my snake injured himself during digestion.

Then yesterday he ate another live mouse. This morning I replaced his bedding and he flipped over and had a very hard time righting himself up again and seems lethargic. I am not sure if he is just tired from eating or sick.

I am not sure if it is just old age, bad mice (from Petco), or neurological. He seems better after a couple days with each instance so I am kind of ruling out neurological. Although he sometimes has trouble catching the mice and has a head sway thing when searching for the mouse and is unable to climb his cage like he use to.

As he is so old I worry that he will choke or have other issues with feeding.

I have always wanted to try frozen mice but my snake is picky and will leave a mouse in his enclosure for days if he doesn't want it.

How often should he be fed? In the winter (in CA!), he hibernates for several months and refuses any food.

Suggestions?