Some things to consider if this happens again- test tension due to straight stitching on top ususally means top tension is too tight. Change needle,check needle to make sure inserted correctly, lower pressure foot and gently pull thread- needle should bend stightly which means top thread is correct in tension guide, check threading on both bobbin and top, make sure bobbin thread and top thread are same or compatible by testing on different material, change all thread and test to see if thread is issue. Lastly take break.