Biting my tongue

Apparently, as I sleep, I keep consistently biting the sides of my tongue, usually in the back, sometimes on both sides, sometimes just one side. It is getting so frequent now that my speech is becoming effected, as my tongue is so swollen and sore from the bites. It is even getting a little hard to eat because of it. Even just sitting here as I type they're are hurting from just hitting the sides of my teeth. Could there be something causing this, or how can I prevent this from happening so often?