Should I be worried?

That's called TMJ or lockjaw. There are a lot of ways to fix it. What happens with TMJ is that the cartilage in your jaw bone is worn down. It's like any other broken bone, it needs to rest. No chewing on gum, or anything super chewy. You need to let your jaw rest. Also, talk to your dentist, there are mouth guards they can make for you to wear while you sleep. This mouth guard lets your teeth/jaw sit correctly while you're sleeping and most of the time solves this TMI or lockjaw problem you're having. If it's worst case scenario, which it doesnt sound like it is, there are a few surgeries that can be performed, most of these are covered by insurance. Put heat on your jaw and call your dental professional tomorrow. They'll know what to do. :)

It's probably nothing serious but I would still recommend having it checked by your doctor or dentist, because in the long run your joints will be damaged which could result in arthritis.

You don't give any information, such as your age or sex, but what you describe is not uncommon. However, if, as you say, it happens with every bite, you might want to consult a doctor or orthodontist.

See your dentist for diagnosis and treatment.... sounds like you are having trouble with your TMJ.

It's a tumor. Just kidding. It's probably nothing and just ask your dentist. He will say it's nothing as well.