Why do men sometimes distance themselves.... and what does this mean...?

Ok... my story! I have been seeing this guy for about a month. We had fantastic first couple of dates, on out third date we slept together, as it felt right. The next time I saw him after that I helped him move house but we never slept together, as I guess I wanted to see if there was more to us then the bedroom. Last weekend out 5th date we went to the cinema... it was lovely, we held hands through the film and went back to his and had a kiss and a cuddle it was lovely, I felt like a kid again! I ended up staying and we had sex then I fell asleep in his arms, it was the perfect night to a fantastic date. The next I didn't hang around to long, just stayed for a cup of tea then went home. I didn't think anything of it! Then I didn't hear form him for a few days, I spoke to him on face book on the wednesday, when he told me his nephew had been born and we was talking about that! Then I never herd form him all weekend! I finally texted him yesterday and asked what he was up to this weekend, he said he had been out friday night and was very hungover so spent all day in bed saturday! " ok I thought"! today I sent him a text asking if he was feeling better and asked if he wanted to meet, he said OK what day is best for you...? so I replied and haven't herd back! His being very distant since the weekend and I'm not sure why...? why do guys blow hot and cold for no reason...? Is there anything I can do or say to this guy? If it was just sex he wanted wouldn't he have done a runner the first time...? A little advice please x