Without a comprehensive evaluation I cannot say for sure, but with many years of experience, I can suggest that you are probably a bruxer. This means that you are clenching or grinding your teeth against each other very forcibly at night while you sleep. Most people don't even know they are doing this and you may feel the same way. A dentist with advanced training can evaluate your mouth and bite to see if this is the problem. The solution is not to just wear a night guard, but to get to the core problem that causes you to do this at night. Many people think it has to do with stress, but while you sleep you are not stressed, so this is not it. There is no mental or emotional component to the cause for this. It has to do with a physical imbalance in your bite that manifests itself more at night. Unless you get this corrected, you will continue to fracture ad break crowns and even natural teeth. You can find a highly trained dentist in your area that has had the advanced training for this by going to pankeydentist.org and search in your area. Good luck!