No idea what happened to my mouses health

Question
I had previously asked this question to Natasha, but apparently she doesnt have vet experience, and according to her, you do, so... hope i can figure out whats wrong with my eldest mouse, so if its something i did, i can prevent it happening to my other mouse.

Recently, hes been exibitting behavior similar to being brain-damaged (i would think....). He moves funnily, clumsily, twitches on occasion, and doesnt really seem to realize that hes moving when hes moving. hes very uncoordinated, stumbles when he walks, and just moves in a way i can only describe as 'funny'. he also cant climb the bars of his cage anymore, and just falls off before hes even gotten his hind feet off the ground. He seems to be eating and drinking just fine, though... but he doesnt appear to be cleaning himself anywhere other than his face (again, very clumsily). he also doesnt notice my presence when i put my hand in the cage (he's ill-tempered and usually comes after me).  He also seems to be peretually sniffing. im not sure if hes actually sniffing, but his heads moving in a rotational movement perpetually, as if he were sniffing, but he doesnt appear to really have control over it.

I have a guess that he may have had a seizure while i wasnt around, and mightve gotten damaged from it, but.. im not really aware of mouse health problems, so its just a guess based off of a few things ive read.

Answer
Has he shown any signs of illness before this occured, such as sneezing, red staining around the eyes or nose? Rodents can develope ear infections, which in turn effect their balance. It is also possible he may have had a stroke as well. Head tilt is common in rodents who have suffered severe respiratory infections. Usually, after the damage is done it is permanent. If he is having trouble balancing I would place him in a tank asap, so that he does not injure himself. Is he eating and drinking? Do you have any exotic vets near you? I would consult with a vet and see if he can be treated. If it is indeed an ear infection treating it quickly with antibiotics (such as Baytril) may help him heal a bit faster, and hopefully not cause any permanent injury to his ear. Though rare, mice can get brain tumors which lead to tremors and seizures.