I have had a pain behind the groin for over a year now. After many tests it has been described as a "lower abdominal muscle strain" by a NHS physio. It is too deep to treat but that is alao a difficult area to treat for obvious reasons. I was advised not to run, but also that doing nothing would be just as bad. This was proved by a period of total inactivity prior to my consultation which I thought would help but made the problem fives times worse. Non-impact training, such as cycling or an eliptical trainer, helps. Basically, anything that does not strain the affected area. So yes time is probally the best cure but do not do nothing. Also, be patient; my problem keeps returning despite everything and I have only raced once this year as a result whereas normally I run 20 - 30 races a year.