Quite a while ago a friend of mine had similar problem after drinking alcohol he was stuffed for about a week being ill, etc. After seeing doctors and some tests it was discovered he had Hepatitus C. Apparently the liver can hide the presence of Hep C with slightly elevated enzymes but not too abnormal.
If you read the media Hep C is said to be the most prevalent around. If looked after people shouldn't have problems and can be quite healthy. Not looking after yourself could result in liver damage.