4 things to check before you panic
Check to see if the clutch knob - the chrome knob in the middle of the balance wheel is tight.
Check to see if the feed dogs have been dropped
Check to see if the stitch length is at 0
Check to see if the pressure foot is adjusted too loosely.
You may have to look in a manual to find how to do some of those things or maybe someone will come along and spell it all out for you.