Anxiety while sleeping

There was always these instances wherein I would just wake up with my heart palpitating, my mind thinking about what I need to do for tomorrow and insisting that I would fail in doing them. Just last night, I remember waking up in the middle of the night, all of a sudden thinking about my Physics homework that is due in three days. I was thinking that I'm going to fail in understanding the topic, even if there's a lot of time to study it. My brain randomly thinks negatively and I have no idea why. I just try to breathe evenly and slowly, but sometimes it doesn't work anymore.