Strange Behaviour

Question
My cat got out yesterday and was out all night he is normally a house cat, He has been acting very strange since he came back he is walking around unsettled and is making a low meow sound, He has eaten and drank but is not his normal self. Normally very playful but now is quite slow and not trying to jump up on furniture etc. Any ideas ? He is 1 years old and has not been neutered.

Answer
Your cat may have gotten hurt while outside. You may not be able to visually see a wound all the time. It also may be that your cat was scared when outside (by an animal or even a human).
Keep the cat in from now on, and when you go to get him neutered, have the vet give him a complete exam. There are so many things that can happen to a cat that goes outdoors, that it is impossible to guess what it may be.
It is always better to have indoor cats anyhow. The life expectancy of an outdoor cat is, at the most, 5 years. Indoor cats can live 12-18 years.