Hi there. These sorts of symptoms can be indicative of a varying range of possible diseases, so i'm afraid it's difficult to be definite about a particular diagnosis- however, these symptoms can sometimes occur in certain vitamin deficiencies- mainly either vitamin B (which controls nerve function) and vitamin C .
Had he been eating well up to this point??
The best course of action is probably going to be to take him to the vets, for a multivitamin injection (if your vet thinks vitamin deficiency is possible).
Other possibilities though, especially considering his young age, are congenital epilepsy, liver problems(which can cause seizures), and certain kidney disorders(which can cause weakness and seizures).
Until you can get him to the vets, i would try and keep him as comfy as possible, and try and syringe some pineapple juice down him for a vitamin C source.
I do hope he is ok.
Regards Andrea
Veterinarian
bvm&s mrcvs 15 years as a companion animal veterinarian