Waking Up In Hip Agony?

A few weeks ago I woke up feeling like someone had pulled my femur from the hip-socket. I cried in agony; staying still wouldn't fix it, moving about made it worse. Today I woke up and it happened in my right hip, and the pain lasted for twenty minutes. I held down my will to throw up with the pain, and walking up or down stairs was impossible. So I was trapped on my bed until I mustered the strength to fight it. The pain fades after twenty minutes like I have said, but it is near impossible to walk properly for an hour. After a few hours, there's nothing but a slight twinge. Has anyone experienced this, and what it could possible be? I'm afriad to sleep tonight in case it comes back with a vengeance, but it has only been the second time on two weeks. I have been trying to sleep on my back to prevent the problem recurring. I am not an athlete, and I have not done strenuous repetitive exercise in my life to cause the the problem.