Relax

I seriously need to learn to relax. I don't understand it. I'm a pretty laid-back, chilled out individual, but physically, I am often tense. I'm even tense during things that shouldn't be. Example: I was lying down a week or so ago, hoping it wouldn't take me 900 years to get to sleep, and I realized my body was not completely relaxed. I had to force myself to melt lol Same thing when I was getting a little bit of massage one day. Even once I'm asleep I'm not fully un-tense. I clinch my jaws and grind my teeth! I've even been told it can sound kind of scary sometimes lol So how do you get un-tense if there is tension even while you are asleep?!