Hi,
Do you remember any stressful incident from your childhood? Have you been to a sleep specialist? If not then please do so at your earliest you may need to undergo a sleep study or polysomnography to diagnose the exact cause.
What has been done to figure out if there is a medical cause to your night time distress? When my severe obstructive sleep apnea was yet undiagnosed, I was having wierd distressing dreams. There are many different sleep disorders, night terrors being one of them, although that would not account for the clenching fists and jaw. The only way to really look at what's going on in your sleep is to have an overnight sleep study at a sleep lab. If that hasn't been done it would be first on my list. What you need to know is if and how much these symptoms are affecting your sleep stages and thus quality of sleep. That's important to know, because if so, you'll need to treat the symptoms. Do choose a reputable facility - ask around. They are not all created equal.
The last thing on my list would be assigning a psychological cause, in fact, it wouldn't be on mine at all. If you suggest that to the wrong doctor, you'll get labeled and maybe never get the diagnostic testing you could benefit from. Don't let those words slip out of your lips except anonymously on here.