Mercury
Don't know what kind of distance you are thinking off and how fast you intend doing it BUT you are running the risk of injury if you jump up in distance too quickly.
But having said that a friend of mine decided to run a marathon on very little training and maximum distance run before was about 7 miles.
She did it in 5hrs20mins with no injury - but she was very, very, very sore for several days.
If you do attempt a big distance make sure you rest enough after it - because if you don't injure yourself doing it, you run an even bigger risk of pulling something (with all the little muscle tears you will have) after it.
take care