Your thread may have popped out of the upper tension discs so re-threading your machine is the best place to start, then start adjusting if that doesn't fix your problem, just like everyone else has already advised.

I agree with Kwiltr. You need to take the thread off and the bobbin out and start over. I bet the thread isn't even going through the tension discs.

I watched a video about getting ready to FMQ that gave this wonderful suggestion. (After you rethread the machine) make a sample FMQ using the same fabric, batting and thread you will use on your quilt. FMQ some lines and circles and record the tension using a majic marker right on your sample. Then change the tension and make a new set of lines and circles. Record again.... and keep changing and checking the results. I've found that different threads can cause a change in the appearance of the stitching so I do this every time I get ready to FMQ on a new project. It has helped me so much to get the best looking stitches on my projects.