What is wrong with my cat?

Could have maybe fleas or mites that is bothering him. Do you give him flea medication regulalry? Check inside his ears and spread the fur on his skin. Can you see any fleas or bugs? Fleas can be hard to see but ear mites (inside his ear) are fairly visible.

My first thought was some sort of head injury but the typical sign for head trauma is a tilted head not a shaking head.

You know you can call your Vet without getting a charge. Advice over the phone is free.

If it is shaking continuously, then you will need to take him to the vet right away as something is seriously wrong. If he shakes it on and off throughout the day, he may have a bad case of ear mites. Look in his ears. Do you see black matter? If so, that is the problem and it is causing him a lot of discomfort. Try the over the counter remedies. They or course are not as good as a vet product, and you will need to apply it for quite sometimes per directions. This may rid the mites or at least take away from all the discomfort. You will need to follow direction to the letter and don't miss a time.

Call your local non-profit animal shelter. Tell them whats going on and they may recognize the symptoms, and if need be they may have a program to help with vet costs. If they do help, ask them for the list of shelter items they need. Something as useless as a towel you were going to throw out would give another stray a bed or help dry a dog before meeting potential adopters.

EAR MITES. Look inside the ears and see if you see alot of black stuff. It is more than likly ear mites. If you see alot of black stuff that means they prolly have ear mites. Go to Wal-Mart or your pet store and get some ear mite stuff... follow directions.. see if it doesnt help.. if it doesnt take him to the vet... YES they will act normal over just ear mites.

I have 6 cats and have had up to 14 at one time. My boyfriends mom has like 40 cats (she IS an animal shelter).. so I know about cats. :)

If he is really old then it is normal