Brother.... Look for an emergency vet. I don't know if he swallowed a towel, that your dog might survive the night. Often (expensive) you can find an emergency vet. If they are not open 24 hours, they will meet you or come to you. If your dog is having any breathing problems or balance that sort of thing, it is even more of a concern. Your dog will likely be okay till the following day. A Vet is necessary to make sure your dog is okay. He may even need surgery.
We just had to have a small piece of towel removed from my dogs atomic. And to give you an idea of size she is a Saint Bernard. Sometimes towels can be passed. She has done it before, but other times they can absorb liquid inside the intestines and become larger. If your dog ate a towel get him to the vet and let take a look. It's expensive, but in our case pet insurance was a life saver. I would recommend it to everyone.
My dog has eaten SEVERAL large socks and small towels. If we are talking a full bath-size towel then you should go get it surgically removed by a vet. Otherwise he will not be able to pass it through the intestine and he will die. Sad but true--my dogs have eaten LOTS over the years and some items have passed through while others (a tennis ball he stole from another dog and swallowed whole) needed removal. It is of key importance to get to the vet immediately as once it hits the intestines and it is too large it may be too late. Hope this helps.